Pageg35 All About Minimums
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Contents
Contents
…Circling to Land; ...Circle
to Land; …Circling Not Allowed;
…Missed Approach; ...More
on Missed Approaches; …Minimums;
…Altitude Call-outs; …Altitude Minimums; …Maximum Elevation minimums; …Below Minimums Part 91 Operations; …Standard minimums; …Personal
IFR Minimums; …Takeoff minimums;
…Zero-Zero Takeoff; …Climb Minimums; …Non-standard
minimums; …Sidestep minimums;
…Obstacle Clearance minimums;
.…Minimum vector altitudes;
…Minimum enroute altitude (MEA);
…Minimum IFR altitude; …
Minimum safe altitude; …Minimums Off Airways; …Minimum
Descent Altitude (MDA); …Descent
Minimums; …Circling Minimums;
…Non-ILS circling minimums;
…Straight-in minimums; …Estimated time of arrival minimums;
… Alternate airport Minimums;
…Minimum Sector Altitudes; …Minimum Safe Altitudes; …Rule
of Thumb; …Normal Landing after
MDA;
Circling
to land
Circling to land is a relatively dangerous maneuver. It contains
the worst elements of IFR flight. There is a minimum obstruction
clearance, a limited space in which to maneuver, an absence of
visual reference, and trying to keep the runway in sight while
preparing to land. At night it is a quite a bit more than dangerous.
The required continuous turn in marginal conditions that keeps
the airport in sight is hazardous. Many approaches that are aligned
with the runway will have only circling minimums. You still may
be able to land straight-in. Set up the missed approach procedure
before beginning to circle. A circle to land requirement is a
contact type of approach or otherwise a visual maneuver done with
reference to instruments.
Because of the hazards associated with circling, flying the airplane
must not be part of the problem. You must know the power settings
and airspeeds that provide some safety margins. Trim the aircraft
for the lightest possible touch. Let go when you look for the
airport. Practice the flying about an isolated airport in good
VFR to hone the MDA skills required in MVFR or LVFR conditions
as for actual conditions.
During training you should make every circle to land approach with as close and short approach as you can handle without exceeding a 30-degree bank and your short field approach speed. This will give you a steep approach. If your circle puts you on a right downwind you might opt (tell ATC) to make a left downwind circle for better visual to the runway. Don't hesitate to take advantage of any wind to get down steeper and shorter. You are required to keep an identifiable part of the airport in distinct view except when concealed by a banked wing.
On an ILS approach you must have a localizer approach with a circle to land option. Most other approaches circle to land minimums published as well and straight-in. Circling minimums only are allowed for all approaches with a letter designation such as VOR-A. No straight-in minimums are published if the approach is more than 30 degrees; off the runway or a normal descent cannot made from MDA altitude. However, you are allowed to land straight in with the runway in sight and an ATC clearance. Request a 360 if you need to get down. In any circling approach keep the runway in sight and stay at MDA until clear of obstructions. If the VOR plate has a runway number it means that the approach is within 30-degrees of the runway and straight-in minimums will be published.
If you lose sight of the runway, overfly the airport, turn to your missed approach heading, and climb. The published missed approach is valid only when begun at the missed approach point at the MDA or higher. You are not promised terrain clearance if you do not follow the published procedure. No turns should be made until reaching the published missed approach point. Any other time you are on your own. The circling minimums presume a high degree of pilot proficiency and familiarity with the airport.
You have planned both the circling maneuver toward the airport and the missed procedure. You have pre-decided, because of the ATIS information, the approach angle sets which side to look for the airport. There are no required circling maneuvers. With ATC clearance you are free to maneuver to a landing as long as the runway is in sight. Requirements of distance from airport center (Category A 1.5 nm) and 300' clearance above obstacles are figured into the circling minimums.
Each category has a different minimum circling radii requirement that is stated in nautical miles for the aircraft category. Conversion of this to statute miles equals the visibility in statute miles as stated on the approach plate. The minimum obstacle clearance within each approach category circling maneuvering area is 300 feet. Height Above Airport. (HAA) is 350 feet for Category A planes. VASI and PAPI equipped runways allow descent when within 10 degrees of interception. Publish minimums provide obstacle clearance only within the protected airspace.
ILS descent must not be below circling minimums for circling to be allowed. If there is a circling approach listed for the airport the circling altitude is the MDA. The MAP is based upon the FAF for the procedure as shown on the chart. An ILS approach for runway 27, circle to land runway 9 has its missed approach point at the designated missed approach point based on DME or on time and is a NON-PRECISION approach.
Every circle-to-land approach is a non-precision approach.
The MDA of a circling approach gives an obstacle clearance of
300' but this is usually still lower than the normal pattern altitude.
Check the charts to see if circling can only be in one direction.
Only losing sight of the field due to banking is allowed. Any
other failure to see the field requires that you start your climb
to the missed-approach altitude, then turn in the direction of
the protected obstacle-clearance region and fly the missed-approach
heading. If you leave the MDA before intercepting the final approach
course the FAA will blame you if you run into anything.
One way to fly circling minimums is to fly the glideslope down
to the published circling minimums for the localizer and then
proceed at MDA on the localizer by timing or DME if authorized.
Another way is to fly the LOC to the straight-in minimums and
landing straight in. If the published ILS approach is to be flown
as a non-precision it makes sense to use the glide slope down
to circling minimums. Basic rule is to fly the shortest path to
base of downwind leg even if requiring you to overfly the airport.
When appropriate all turns should be to the left.
Since a high descent rate usually has circling minimums only, you must be proficient in getting down quickly and in cleaning up during the missed. If you become visual with the runway by knowing where to look for the runway and are using a created VDP a straight-in is possible. Use no more than 30-degree banks in turns and do not rise above MDA by more than 50 feet. Only normal maneuvers are allowed during descent from MDA. If at any point you lose visual contact with the airport and runway you must execute the missed. Don’t depart from the electronic glide slope until within one mile of the airport.
You could use a 90 left/270 right course reversal in a circle
to land situation if conditions require. If possible, the turns
should be made in the direction that gives the pilot in command
the best view of the runway during the turns. Unless otherwise
directed, the AIM procedure, if you lose sight of the runway,
requires you to execute a climbing turn back to the landing runway
and continue the turn to establish yourself on the published missed
approach course. You are required to miss the circling approach
when an identifiable part of the airport is not distinctly visible.
If ceilings permit fly higher than
MDA. A single pilot forced into right turns should not be circling.
The circling approach area is determined by approach category ("A" for C-172). It is a series of arcs 1.3 miles in radius using all the runway ends and sides at the airport. Its size is the largest area possible made from these arcs. Category B is 1.5 miles. Primary obstacle clearance is only 300'. If obstacles are in the way no circling will be allowed. Obstacles of less than 400' may not be charted on the plates!!!! Circling in a specific direction may not be allowed. Study the chart. Occasionally it is necessary to remain at a higher than published altitude when transitioning to the approach. Occasionally, even the minimums vary according to the approach category. If the descent requires you to fly at a higher approach speed you must use the minimums for the higher category. Likewise, you must fly the missed approach published for the higher category. Obstacle clearance is assured only when using higher minimums for the speed flown. Higher minimums apply if an aircraft is flown at a higher category airspeed.
FAA figures a 400-fpm descent rate for the full approach but when circling is required the 400 fpm applies only to the MDA. A higher rate may be required below the MDA for the straight in approach. Don’t force it. Let the tower know if you do not plan to make a straight in. The PTS in Task E of the instrument approach procedures requires that an applicant know all the elements of the circle-to-land procedure. In a 22 word sentence the PTS says that the pilot must check the wind. At an uncontrolled airport this means to overfly the airport and check wind indicators. Basic procedure are to fly to the specified minimum, only if in visual conditions you circle to land on the designated runway into the wind. You are not allowed to descend below minimum altitude, go below visibility criteria or make other than a normal landing.
The circle is after ATC authorization when a straight-in landing is not the preferred option. Even if cleared for a straight-in you can circle only if you have not descended below the circling minimum. You have obstacle clearance if you remain within the radius of your approach category based only on your normal approach speed. The only way the examiner can participate in the flight is by maintaining a traffic watch. The missed approach instructions are based upon a straight in landing.
Since the circling approach will be coming in from nearly the
opposite direction the direction of the missed turn will be
reversed from the one published. The way you fly the circle is
more apt to cause an accident than the weather. Circles are
hazardous because you are low, slow, and turning. However, you
are more likely to fly into the ground while on the
centerline. Don’t circle if there is another option like
landing downwind. Don’t circle with ice aboard. Don’t
bust MDA.
Use shallow banks. Never change from your decision to make the
missed. A good missed is preferable to a bad circle.
Regardless of the clearance, every missed approach begins with
a straight-ahead climb with sufficient time to configure
before initiating any turn.
--63% fatal
--51% stalls
--31% icing
Circle
to Land
A circle to land in daylight is bad but circling to land at
night is worse. Because two different procedures are involved.
During the day the circle to land is actually a contact approach
in which you must keep the runway in sight while remaining
clear of clouds. At night the circle requires that you remain
clear of clouds and below any ceiling. You do not have time to
scan the instruments if you are watching the runway. It is best
that you keep your speed up until lined up with the runway.
Once you lose the runway, turn to the runway and go for the
published missed. If you haven't briefed the missed you are in
considerable do-do. If you are not well prepared for the missed
it is best to avoid making the circling approach. Go missed
before you reach the airport by climbing to the MAP before making
any turns. Do this because it does not require the flying
skills, the planning and situational awareness that must be part
of any circling approach or missed. Don't go near an icing
situation during a circle to land.
Circling
Not Allowed
A circling approach cannot be made if straight in descent
has gone below circling minimums. Any circling must (should) be
to keep the airport and runway to be used in sight from the pilot's
side. There are no circling minimums for an ILS approach. Minimum
descent altitudes may be published for straight-in-landings, circles-to-land
or both. Don’t use a lower straight in minimum for a circle
because the 250’ obstacle clearance only applies to the centerline
of the approach. Because of obstacles the direction to circle
may be restricted to higher minimums. Read the chart notes.
Missed
Approach
While the preflight preparation included a complete run-through
of the missed procedure, a review is done outside the FAF perhaps
by noting the procedure written in crayon on the windshield. The
prepared student asks questions about radio settings, identifiers,
and any changes from ‘as planned’. Among the vitals
of position awareness are your equipment
settings.
You already have the missed checklist out. At the missed you must have pre-decided the sequence of events that you will perform. In addition to the sequence you have pre-decided the timing you will use. Talking is way down on the list. Get the power in, go to the heading, set pitch attitude, and remove some flaps. Gear later, talking later.
A mandatory reporting point. The IFR missed approach is more demanding that a VFR go around because it will occur in IFR conditions. The first consideration in low IFR conditions is to relate these to your personal minimums. If a missed approach is a possibility, it would be best to hand fly the approach instead of using autopilot. Controllers may be unfamiliar with where a Missed Approach procedure goes. The published missed approach is often a non-radar procedure and not very efficient. The missed approach course usually approximates the approach course. If you forget the missed procedure, add full power and climb on runway heading.
We often become slaves to our training and fly the total time to the missed approach. Rather, at our personal minimums and Visual descent point we would execute the missed. Get away from the ground and obstacles, climb on course and don't turn until the published time runs out. Don't clean up the plane until everything is under control. Since you have memorized the first part of the missed approach procedure and radios are pre-set you don't need to refer to the plate. Don't do anything in a turn during the climbing missed except control the turn.
Should you experience a full CDI deflection at any time you can climb but you MUST not turn before reaching the missed approach point. There is no guaranteed obstacle clearance protection beyond the full deflection of the CDI until we reach the missed approach point. An early turn may present obstacles that exceed your maximum climb rate.
You are likely to make the mistake of not applying full power only once. Power comes first, then pitch, positive rate, gear and flaps. Any change in the order is going to be exciting. Every missed starts with a climb. If you happen to have dual navs set them both to the approach. The other option, of using the second nav for intersections or missed or for distance means that re-setting is required. This distraction may (will) create problems. With flip-flop nav critical fixes become relatively easy.
The ILS missed approach point is a given when the glide slope meets the decision altitude. If you are inside the marker don’t try to salvage a poor intercept. Some say not to time for a localizer approach if it detracts from the ILS. Fly one approach at a time.
VDPs (Visual Descent Points) are not charted when DME is available or when there is no local weather advisory. The VDP gives a charted point from which to commence a normal landing approach with the runway in view. Use of the VDP is discretionary. While there are complex ways to use the DME to find the VDP for normal and possible landing slope to the runway the easiest way that will work consists of: Take 10% the MDH, subtract that number in seconds from the approach time. At that time, if you do not have the required runway visual indicators commence your missed approach climb and turn when the time runs out. This method flexes and works for both altitude and airspeed differences.
For the straight-in non-precision approaches nothing beats having a pre-planned visual descent point. There are several ways of getting a self-made VDP. The easiest way is to take the MDA (HAT or HAA) and drop the last digit. Use the remaining figures (2) as seconds to be subtracted from the approach time. The 3-degree descent rate usually desired can be obtained by multiplying your ground speed by five. At 100 knots a 500 fpm descent is close to a three-degree descent.
Missed approaches do not occur often but the missed approach should be a part of your proficiency training after you have the rating. Get to a safe altitude before you become upset with the weather forecast, ATC or yourself. The unexpected missed is the most difficult IFR procedure of all. It will be much harder if some instrument fails at this time. Use your no-peekies on the missed for practice.
The missed approach has several problem areas. Following an incorrect procedure can fly you into an obstacle at worst and at best may not return you to the correct fix. An approach flown too far due to failure to determine the actual ground speed creates a distraction problem. Looking for the airport is the most usual accident causing distraction. A mistake in your ground speed that makes you look for the airport after you have already passed it can be a fatal distraction. Use the ATIS wind direction and speed to predetermine the indicated airspeed you will use on the approach.
Preparation for the missed begins with the weather. An ATIS can be up to an hour old. I would suggest never making a nonprecision approach if the weather makes the outcome doubtful. Except for training purposes successful non-precision approaches in minimum conditions will create dangerous habits and presumptions. Save yourself the aggravation and proceed to a precision approach facility.
The stress level of a second approach after the missed approach is much greater than for the first. If the miss is because of procedure or technique, you could try again. If the miss is because of weather, find an alternate. The temptation to go below your personal minimums is greater on a second approach. The second approach has a disproportionate number of fatal accidents.
AN ATC warning of course or altitude DEVIATION is sufficient
notice to begin THE MISSED. If you do not continue to fly the
course procedure until the time has run out you will not have
guaranteed terrain clearance. Do not turn until past the missed
approach point. A climb is allowed but no turns.
More
on Missed Approaches
Some characteristics of an emergency exist in the missed approach.
Far too many practice instrument approaches end in
the missed instead of landings. The instructional reason most
often is to avoid the ground delays occasioned by the full-
stop. Just lately, to avoid such a delay contained in a warning
by ATC, I opted to have a student enter a holding pattern.
At the end of our eventual missed ATC thanked us for the help.
Nice. However, since most not for practice approaches
end in full-stop landings, such landings are much to be preferred.
The ideal IFR program would control the weather so
that all lessons could progress from near VFR conditions into
low IFR conditions. Since my wife only controls the
existence of head winds (always), I must adapt to the variables
that exist in the real world.
According to the FARs, you must have only three variables under
control to avoid the missed.
First, you must be able to make a normal descent to a landing.
Second, you must have a visually identified runway, runway markings
or lights
Third, you must have the minimum flight visibility required for
the procedure.
Recognition of these requires judgment that is best acquired
by experience. This experience requires that you plan in
advance as to how you will perform to the specific conditions
as they exist. For the non-precision approach you must
come up with a visual-descent-point plan, know where to look for
the visual runway clues, and know references for
visual distance. For the precision approach there is no need for
a visual-descent-point, it is best that at some point on
the approach, say inside the inner marker, that you slow up and
configure for landing. Runway behind you has no value.
While the DH of the ILS will allow a normal landing if you
have slowed up, the MDA of the non-precision approach allows
no such option. If you reach the MDA you will not be able to make
a normal landing. You must accept the necessity for
the circle-to-land procedure. You can decrease this necessity
by getting to the MDA as soon as possible to increase your
visual reference margin. Flying a slower approach speed is another
way to avoid the circling approach. It helps to know
the length of any lighting array and runway you are using. These
should be a part of any pre-approach briefing.
Minimums
Some minimum altitudes are published on charts. The published
minimums are designed for the competent pilot. If you are less
than proficient raise the minimums. Other minimums are only
published for controller use. It is possible to request a lower
than published altitude, if it exists it may be authorized. Such
distinctions exist where flight along VOR to VOR routes have published
altitudes but a vector airport to airport may allow a lower altitude
via RNAV or radar vectors.
IFR airspace flows with the terrain. Minimum IFR altitudes in feet MSL are based upon obstacle clearance. Approaches are based upon descent angles, maneuvering area, aircraft speeds, etc. FAR 91 operations have no landing minimums but according to aircraft and pilot capability the safety of FARs 121 and 135 should be followed.
You must plan any flight with knowledge of the underlying terrain.
A vector may take you uncomfortably close to the terrain. ATC
has been known to assign headings and altitudes that precipitate
CFIT (controlled flight into terrain) accidents. As the ultimate
responsible party you must keep aware of your terrain proximity
and clearance.
Altitude
call-outs
--Stepdown altitudes
--Where am I, cross-check?
--No delay of missed
Second Pilot
1. Confirms briefing data
2. Calls alltitudes
3. Calls missed
4. Calls runway
Altitude
Minimums
ATC expects you to hold right on assigned altitudes as per
FAR 91.123 regarding clearance deviation. In terminal areas ATC
has a 200 foot margin before they get on your case. This allows
for turbulence and altimeter errors. Center and terminal rules
have longitudinal, lateral and vertical minimums that vary somewhat
if in radar or non-radar environment. Laterally in terminals it
3 nautical, in centers it 5 nautical with radar. Without radar
it varies. Aircraft given vertical separation above 10,000 get
merging traffic calls regardless but below 10,000 ATC is not required
to give a call.
By asking for a visual climb, descent or separation the pilot has agreed to maintain VFR and visual separation. ATC likes this because it relieves them of responsibility.
At some point, in every young persons education, it is usual to explain the facts of life. Such is also typical of IFR instruction. At some point an instructor must reveal to the trainee that the bending of an occasional FAR minimum varies from questionable to suicidal. Most such violations are deliberate. FAR 91.129 Applies to aircraft on an ILS approach. It says that pilots are expected to remain at or above the glideslope as indicated by either the ILS or the VASI. No glide slope will intersect with an obstacle. Getting closer than the DA on an approach almost any fly-up indication could mean that there is an obstacle in your future. Maximum risk is inside the DH which is 200’ above the touchdown zone not the terrain below. Obstacle clearance may be as little as 120 feet. In a step-down approach you have a margin of 250’ obstacle clearance.
Your best way to handle obstacle clearance below MDA or DH
is to use an existing or make a visual descent point, either by
time or by DME. At three-degree glidepath intercepts these at
a visual descent point. Most actual approaches do not reach minimums
before breaking out. Slant range visibility is more important
on an approach than vertical visibility.
Maximum
Elevation minimums
Terrain figures for chart purposes are rounded off the nearest
100 feet and then 200 feet is added. The chart figures thus makes
the elevation with a safety factor of from 201 to 299 feet. For
obstacles made by man the figures are rounded up to the nearest
100 feet and then another 100 feet is added. The safety margin
is then from 101 feet to 199 feet. The pilot is well advised to
add some more.
Below Minimums
Part 91 Operations
Under FAR Part 91 flight rules:
--A 24 hour monitored ASOS at an airport will allow for alternate
minimums
--Any type of FAA approved weather forecast may be used to determine
if minimums are met under FAR 912.169(c),
including Area Forecasts.
--Ceiling not a factor
--Visibility as determined from the aircraft is key factor.
This flight visibility can not be less than required by procedure
--No descent below DH or MDA unless:
1) Position to make normal landing, and
2) Approach light system; threshold markings; runway end identifier
lights; VASI; touchdown zone, its markings; or its
lights or runway, its markings, or its lights are visible and
identifiable, and
If 1) is missing a missed approach is initiated, or
If 2) not even one of the features is visible and identifiable
a missed approach is initiated.
The FAA investigates all IFR landings made where below minimums visibility is reported. I suggest that you have difficulty hearing any ATC request for your flight visibility after an approach.
Standard
minimums
--For a precision approach (glide slope) 600' ceiling and
2 miles
--Obstacle clearance for precision approach is 121’ trapezoidal
area tapering to runway.
--Obstacle clearance on intermediate segment (procedure turn)
is 500’
--Obstacle clearance on feeder and transition routes is 1000’
+ depending on terrain.
--For a non-precision approach 800' and 2 mile visibility
--Obstacle clearance is minimum of 250’ trapezoidal area
with no greater clearance in any one area over another.
Procedures with a FAF all have 250’; a VOR without FAF is
300’; NDB with FAF is 300’ and without is 350’.
--Obstacle clearance on intermediate segment (procedure turn)
is 500’.
--Obstacle clearance on feeder and transition routs is 1000’
+ depending on terrain.
--FAR 91.l15 allows descent below DH or MDA to TDZE+100 with any
part of the approach light system in sight. To
descend below TDZE+100 requires having the terminating bars, siderow
bars etc. in sight.
Personal
IFR Minimums
Every pilot who has flown into unexpectedly low IFR conditions
has come away with an appreciation that it is necessary
for him to set personal limits for his IFR flying. Every IFR flight
has to be weighted with the pilot's evaluation of his skill
and experience, familiarity with the aircraft and instrumentation,
local awareness of terrain and obstacles, and the 'need' to fly.
A second pilot in front with you is always a good idea. The
unexpected on takeoff that prevents a return due to below
minimums weather, requires an immediate flight to the nearest
safe haven. The setting up of departure and arrival
procedures can always use another pair of hands and a mind as
back up. Single pilot IFR is very lonely. Any departure
from a field that cannot be returned to is certainly challenging
the Gods.
Parts 91.167 and 91.169 spell out the minimums that must exist
one hour before until one hour after your ETA at original
destination must have 2000' ceiling and three mile visibility.
Should conditions be lower you must have an alternate airport
with precision approach limits of 600' and two-mile visibility
or a non-precision approach with 800' and two miles. IFR
Fuel requirements apply.
The safety of a specific flight at any specific point of this flight is directly related to the selection of options you have available.
Takeoff
minimums
Set radios for the IAP for the other end of the runway. An
even better might be a GPS or VOR approach to a crossing
runway. Part 91 can depart but other Parts cannot depart if conditions
will not allow a return to departure airport. If
conditions are below landing minimums but above takeoff minimums
we must have an alternate airport that is within one-
hour flight time. Taking off in zero-zero Part 91 is legal but
you must know where you will go if something stops working.
Takeoff minimums are not mandatory on FAR 91 operations but the
Part 91 pilot should be aware of the FAR 121,129 and 135 minimums.
A chart may show takeoff minimums and still not have an IFR departure
(Not Part 91)
Zero-Zero
Takeoff
There are no accident figures that preclude zero-zero takeoffs
as being dangerous. The acceleration of the aircraft can cause
a somatogravic illusion that you are more nose up than it seems.
Pilots who habitually make zero-zero Part 91 departures tend to
be confident of their abilities and the maintenance of their aircraft.
The risk in a low-visibility takeoff lies in loss of control. Control can be lost during ground acceleration or in the transition from seeing the ground and entering MIC. You do not have any prep-period for the instantaneous change. Acceleration is a vertigo producer and the pilot must know that illusions will occur and gauges must be believed.
The next immediate risk is loss of power. Even if you know
the area, low-visibility blinds you and trusting to blind luck
is not a good choice. It is for these reasons that the airline
minimums of one mile visibility are good minimums for the Part
91 pilot, too.
Low visibility takeoffs and departures have as an inherent factor
flight close to the ground and unseen obstacles. The hazard of
the takeoff is the abrupt transition to a full IFR workload. Part
91 has no minimums for takeoff but as with any other IFR takeoff
it has four phases:
(3)Liftoff;
Rotation speed should be slightly faster than usual and relatively
positive and smooth. Let the plane fly off and get on the gauges.
Apply right rudder. Get at least 100' before changing gear or
flaps. Waiting longer is usually better.
(4) Initial climb.
Maintain two bars on the AI and confirm airspeed and VSI both
of which may lag due to static error.
Climb
Minimums
FAA climbs and climbs to minimum altitudes are predicated
on crossing the departure threshold at 35'. You are required to
report to ATC anytime you are unable to climb 500 feet per minute.
Non-standard
minimums
An airport that meets the weather forecast may not be legal
if it has non-standard minimums. (Jepp on airport diagram sheet).
A NOS chart may show an A for an airport where Jepp charts
may not because Jepp does not chart for Category E aircraft.
Sidestep
minimums
Sidestep landings to parallel runways have higher minimums
than straight in approaches. Sidestep should be done as soon as
runway is in sight.
Obstacle
Clearance minimums
Obstacle free zone (OFZ) May be used in specific region near
airport.
From end of runway away from MAP you have 1/2 nautical mile obstacle
clearance area. This area extends in an ever widening angle to
13.5 NM. At 13.5 NM the primary safe area extends 4 nm to each
side of center line and the secondary safety area is an additional
2 nm to each side.
MOCAs insure obstacle clearance by 2000' lateral and 1000'
vertical and navigational signal within 22 nautical of Navaid.
In some instances as over the hills of Vallejo and Hayward the
proximity of the terrain is much closer.
--Every airport with an instrument approach procedure also
have a departure procedure if obstructions are present in the
terminal area.
--An IFR departure is available for safety when terminal area
obstructions cannot be seen or avoided.
--Obstacle clearance is assured if the departure end of the runway
is crossed above 35’ and climbs to 400’ before turning.
--At this point a climb of 200 fpm will clear obstacles up to
the enroute airways.
--This and any published rate of climb will clear obstacles by
35’.
--NOS charts have a T to advise of non-standard requirements.
--90 knots per nautical mile gives a climb rate per minute of
300 where only 200 fpm may be required.
--If 350 fpm is required you should climb at 525 fpm.
--If terrain is above runway elevation the obstacle clearance
may be a little as 120’ even though the DH is at 200’.
--The further away from the runway the greater the obstacle clearance.
--Laterally the protected airspace is 1000’ wide when 200’
from the threshold.
--At ten miles the lateral dimension is five miles to each side
of the centerline with the outside mile tapered upward.
--Your obstacle clearance may be as little as 70 feet.
VOR/DME with FAF, Straight-in 250 250
VOR/DME, radial or arc final 500 500
NDB on airport, no FAF, straight-in 350 350
NDB obstacle clearances become wider toward the runway. This accounts
for the higher minimum descent altitudes
NDB w/FAF, straight in 300 300
Localizer, LDA, SDF 250 250
GPS approaches usually become narrower toward the runway. Therefore,
the MDAs are lower. Cannot be used to track
courses unless there is an overlay. It is o.k. to fly the missed
or a transition but not the approach.
Circling 300 Tapers to 0
Holding 1,000 500DF Approach 500
In the secondary area the obstacle clearance tapers to zero at the outer edge. The greatest clearance is on the centerline.
Approaches with 500’ minimums will have higher obstacles. Check the circling area.
If you intend to land, you must at some point descend below the
MDA and DH. The closer you get to the runway the less your obstacle clearance becomes. The non-precision minimum is 250’. The visibility minimums of all approaches are determined by the slope to the runway. It is possible to have an obstacle intrude into the glide path inside the DH if visibility minimums are over one mile.
Minimum
vector altitudes
Controllers are required to issue an altitude to maintain
that provides obstacle clearance until on a published segment
of the approach. MVAs are used by radar controllers depending
on radar quality and the distance from the antenna. Controllers
often put in their personal fudge factor to protect themselves.
Minimum
enroute altitude (MEA)
The MEA provides at least 2000' of clearance above enroute
obstacles when the route is over mountainous terrain and 1000'
otherwise.
--An MEA assures reception of VOR signals. VHF communications
are usually but not always possible.
--MEA guarantees radio communication on airways. Communication
is guaranteed at FAF and as missed approach point.
There is no assurance of communications anywhere else during the
approach.
--Don’t accept as gospel the MEA altitude during very cold
conditions.
--Request or fly at least a thousand above MEA.
Minimum
IFR altitude
The MIA is on unpublished direct ATC routes established by
the facility. Any ATC clearance will give restriction to keep
pilot above MIA.
Minimum
safe altitude
If there is no nav facility within 30 nm of the airport, there
will be no MSA. MSA provides 1000' clearance above the highest
obstacle in a defined sector. Be sure to check plates to see facility
used to determine MSA distances.
Minimums
Off Airways (Jepp MORA /FAA OROCA
IFR pilots operating on an IFR flight plan off a designated
airway must ensure they operate at a safe altitude based upon
the requirement of FAR 91.177. Actual flight information can only
be determined by use of sectional plus any NOTAMed new obstacles.
The pilot is responsible when operating off-airways on a direct
routing for determining the minimum en route altitude. In mountainous
terrain the minimum IFR altitude for off-airway operations is
2000' above the highest obstruction within 4 miles either side
of your course.
Minimum off route altitude. On Jepp shown at 6000' or lower gives
obstacle clearance of 1,000'. Above 7000' there is 2000' clearance.
This is only obstacle clearance no reception or navigation included.
NOS Off-Route Obstruction Clearance Altitude (OROCA) and Jepp's
Minimum Off-Route altitude (MORA) are supposed to provide obstruction
free direct routes. These altitudes are the same as appear in
each quadrant of the sectional charts.
Minimum
Descent Altitude (MDA)
As written by the FAA the lowest altitude, expressed in feet
above mean sea level, to which descent is authorized on final
approach or during circle-to-land maneuvering, in execution of
a standard instrument approach procedure where no electronic glideslope
is provided.
Simplified:
Lowest mean sea level altitude during non-precision approaches.
This is one of the most dangerous flight altitudes in all aviation. Single pilot operations that require the pilot to find the runway indicators make the presence of an flight ‘looking’ assistant very desirable.
Descent
Minimums
You cannot deviate from the published approach procedure unless
you are in VFR conditions and you have canceled IFR with ATC.
The published IFR altitude for a final approach segment is the
minimum descent altitude. (MDA)
Requirements for descent below Minimum Descent Altitudes. (MDA)
1. Aircraft in position to make normal approach and landing
2. Approach threshold or approach lights or other airport markings
are visible to pilot.
3. Flight visibility is not less than prescribed visibility for
the approach.
4. Arrival at missed approach point or thereafter requires both
1, 2, and 3 above or a missed approach must be
commenced. FAR 91.175
5. Doing the published approach may give lower (ice free) altitudes
than taking vectors due to vector minimums.
#1 of the above creates a particular problem for non-precision
approaches where the runways are typically shorter than for
precision approaches. Any excess airspeed carried in the approach
but not required for landing must be dissipated. Diving
for the runway will not work. The placement of the non-precision
missed approach point precludes a normal landing unless
the landing decision can be made prior to reaching the missed
approach point.
It is usually considered better to be at the MDA well before you
reach the missed approach point since it allows you to
design a VDP from which you will be able to perform a normal landing.
An additional advantage is the stabilized level
arrival allows more time for creating the best landing configuration
ahead of time with sufficient time to configure for the
missed approach. If you can't make a normal landing you will be
below the circling minimums.you must execute the missed.
Having the missed approach point at the end of the runway will
preclude the making of a normal landing approach unless
the runway is over a mile long.or if a strong headwind exists.
Time and airspeed must be under control or serious problems
of decision making will arise.
MDA and MAP Revisited
The critical time of instrument flying occurs on the
approach. There is little room or time for the reading of charts,
looking
for frequencies, repeated communications, verifying altitude or
to make repeated adjustments to power or headings. There
are an average of 35 approach accidents every year that seem to
derive from the pilot who gets distracted by these elements
of preparation and repetitive activities that need not occur.
Let us consider the MDA, that is the lowest altitude, expressed
in feet above mean sea level, to which descent is authorized
on final approach or during circle to land maneuvering in execution
of a standard instrument approach procedure where no
electronic glide slope is provided. Every nonprecision approach
has several MDA as determined by the approach category
of the aircraft. The circling radius is also determined by aircraft
category. Flying an approach at 100 knots moves the
aircraft into category B. The required standard rate turn angle
of bank also increases with each speed category.
There is good reason never to attempt a circle to land at the
straight in MDA. You will not have obstacle clearance while
circling. The MDA increases as approaches lack precision ranging
from 250 feet to 500' for the DF approach. If
precipitous terrain, remote altimeter setting, of extended final
approach course exist an additional 350 feet will probably be
added. Additional limitations may apply for night or excessive
descent rates.
Using the MDA, such as exists at Concord, CA, of 380 feet an
aircraft one mile from the threshold at an approach speed
of 90 knots would need 1.5 x 380 =570 fpm descent rate; at 120
knots the descent rate would be 760. Such high descent
rates often result in getting below the MDA and into obstacle
territory. Obstacles are permitted within one nautical mile of
the final approach fix inbound up to a 7.1 descent plane which
intersects the FAF at least 500' below its minimum altitude.
This means that your descent after the FAF must not be excessive
prior to reaching one mile inside the FAF and prior to
the missed approach point.
The reality of the nonprecision approach is that the pilot
should plan a descent rate that gets the aircraft to the MDA
sufficiently before the missed approach point to time in a VDP
beyond which the missed approach is a given. I do this
as a standard practice. It means that my 'personal missed approach
point' exists well before the charted MAP. I do
this very simply by converting the MDA into seconds by dropping
the last zero and subtracting it from the approach time.
For example, the approach time into the Concord LDA approach is
2:16 and the MDA is 380. 38 seconds from about
1:45 which gives me the time at which if I don't see the required
airport visual references I initiate my missed approach
climb. It is my personal experience that the temptation to sneak
lower or force an unsafe descent rate can be so over-
whelming that the early missed is the desirable option.
The alternative to the early arrival at the MDA is the planned
rate of descent to arrive at the MDA just when the approach
time expires. The stated advantage of this method is that the
approach and configuration is stabilized with a corresponding
reduced workload. On a longer runway this would work just fine.
On the shorter runways you may be tempted/forced
to dive for the runway at the last second. Weather information
may help you select this as an option. Figuring in a tailwind
may complicate things. My selection would be to always be at the
MDA before reaching the MAP.
I plan my descents to be at the MDA and stabilized level at
the MDA about halfway between the FAF and the MAP. At
CCR this gives me a mile and a half to descend to the MDA and
a mile and a half to reach the charted MAP Using the
figures from the previous paragraph I would be at the mile and
half point in one minute and eight seconds. Subtracting
the VDP time of 38 seconds would give me 30 seconds to locate
the runway before going missed. Works for me since
I configure the aircraft for landing at the FAF.
There is an often-confused distinction between 'straight-in
minimums' and the straight-in approach. The straight-in approach
does not authorize a procedure turn unless ATC says so. Straight-in
minimums relate to any procedure that is aligned within
30-degrees of the runway heading without an excessive rate of
descent. Not meeting these two conditions, angle and
descent, requires only a circling approaches to be charted. However,
if the runway visual criteria of Part 61 are met for
making a 'normal' landing a straight in may be made. Such a situation
exists on the VOR approach to Hayward, CA.
The execution of the missed approach is just as critical as
is the approach. You can initiate a climb before the missed
approach but no turn should be made before the MAP or as charted
on the plate. The problem in this non-precision
approach is that the time of the turn may be critical.
Often the problem with time relates to the 'landing expectancy'
of
the pilot. Pilots do not usually depart without the expectation
of landing at the selected destination. The 'failure' of the
approach is not a part of the pilot's expectations. Training should
include real and unexpected missed approach events.
Circling
Minimums:
1. Do not descend or use flaps until on final
2. Any airspeed greater than 91 kts raises your category.
3. Lose sight of runway--GO AROUND by flying runway heading in
a climb. You must have an identifiable
portion of the airport in view visible to the pilot while above
the MDA.
4. Only circling minimums are published in a letter coded approach
(VOR-A) straight-in minimums are not
authorized but if conditions allow you may land straight-in.
5. You do not need to worry about other aircraft inside the circling
maneuvering area when in Class D airspace.
6. You may well be concerned about other aircraft when flying
circling minimums at an uncontrolled airport. Left
patterns unless contra indicated.
7. Circling at night is more dangerous than during the day.
8. Do not descend below MDA until on base leg. If at an unfamiliar
airport fly the MDA of the class D aircraft for greater flexibility
and obstacle avoidance.
Non-ILS
circling minimums
One way to fly glideslope down to localizer circling minimums.
Then proceed at MDA on the localizer by timing or DME if authorized.
Another way is to fly the LOC to the VDP and landing straight
in or fly the ILS to the circling minimums for the circle.
Straight-in
minimums
A straight-in approach has minimums of alignment and descent.
A descent gradient of 300' per mile from the FAF to threshold
is standard but 400' can be used. The approach course must be
within 30 degrees. Some straight-in approaches have only circling
minimums because of obstacles. If visibility allows you see the
runway requirements at the circling minimums you can land straight-in.
You should have a VDP pre-decided in such an event. A straight
in approach mandates than a procedure turn may not be performed
unless a specific clearance is obtained.
Non-precision criteria for minimums can have obstacles above the MDA within one mile of the approach fix. Chop it and drop it procedures are not ALWAYS the best way to fly. A straight in may have only circling published minimums if the approach will not allow a normal descent. If you maintain the circling MDA and can make a straight in without excessive maneuvering or rate of descent, get the clearance and do it.
Estimated
time of arrival minimums
If you find your ETA to a fix is going to be off by over THREE
minutes you should advise ATC. The safest ETA estimates seems
to be "6" minutes.
Alternate
airport Minimums
FAR 91.103 says that pre-flight includes knowing runway length,
aircraft performance and alternatives available if the planned
flight cannot be completed. FAR 91.167 adds fuel required to destination,
then to alternate and then for 45 minutes. Based on these FARs,
especially FAR 91.169, an alternate (plan)is required for all
IFR flights except when destination has an approach and is forecast
to be 2000' and three.
An approved alternate must have weather reporting (It can be an area forecast) and the instrument procedure must be continuously monitored. If an airport is not authorized as an alternate one of these factors is probably missing. Where a planned alternate has more than one approach, one of them may be listed as NA as an alternate. The airport can be used only if another approach is used.
Required if not:
Standard 600'& 2 precision; 800' & 2 non-precision. Requires
operating weather observer on site or AWOS/ASOS
Mnemonic: ABCD123 = 1 hour After/Before, Ceilings 2000', Distance
3 miles.
Non-standard
Published in DPs, STARs, Terms and Tables.
On an IFR flight plan into an airport without an instrument approach,
you MUST have an alternate regardless of weather.
The prudent pilot sets his sights on the "filed paper' alternate early on. If the ceiling is forecast at the destination to be less than 2,000' AGL and visibility less than 3 miles, an alternate is required. A terminal forecast (not Area) is required for determining alternate weather minimums. "Occasional implies 50% chance or greater and "chance" is less than 50%.
Terminal weather observation and reporting facilities must be available for the airport to serve as an filed paper alternate airport. If the weather is good as, required in FAR 91.169 to descend from MEA and land in basic VFR, all you need for planning is an area forecast saying so and a runway. Even when an alternate is not required you must have options in mind.
ATC has no record of your filed alternate option. As a Part
91 pilot you should have immediately at hand a takeoff alternate
with plates available. The idea is that if you can't return to
your departure field you should have a near-by airport available
as an real emergency as required alternate. (Locally I would consider
Angwin, on a mountain top near Napa, as a good avection/ground
fog choice for VFR conditions) The ultimate alternate is to cancel
and try an emergency at Travis using their radar assistance. Your
life should be worth the paper work.
Minimum
Sector altitudes
MSA give 1000' obstruction clearance within 25 NM including
mountains. MSA is measured from markers on ILS approaches, the
NDB on NDB approaches and runway threshold on GPSs. MSA does not
apply in mountains, which require 2000' obstacle clearance.
Minimum
Safe Altitude
The Minimum Safe Altitude (MSA) circle has nothing to do with
the approach or the initial approach altitude or the approach
segments or the procedure. The MSA is for emergency purposes only.
Minimum vector altitudes (MVA)are usually below the MSA. The required
obstacle clearance (ROC)of the TERPS procedures for making an
instrument approach procedure also set that the ROC of the MSA
must be 1000’ higher than any obstacle within the circle.
The MSA circle may be divided into sectors for any approach except
for the GPS approaches. The MSA is essentially a non-functional
part of the approach plate.
Rule
of Thumb:
Take half of your ground speed and add a zero. Read result as
fpm descent rate for a 3-degree slope. As with so many things
about flying, getting away with a descent below minimums may be
the worst thing that can happen to you. Just because something
like this works at airport A is NO reason to believe it will work
at B. Obeying minimums is a guarantee that you will live to fly
another approach.
Normal
Landing after MDA
If you shoot a non-precision approach at MDA and time, it
is unlikely that you will be able to make a normal landing. The
nose will block your view of the runway at the missed approach
point. Your legal options are to apply flaps early to
improve your ability to see the runway. The more flaps you use
the better you will be able to see the runway and the lower
will be your stall speed.
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