Pageg3 IFR Instruments
Return to Whittsflying
Return to IFR Contents
Contents
…; Turn Coordinator Vs Needle; ...Attitude Indicator; ...Attitude Indicator Errors; ...AI Demonstration; ...Turn Coordinator; ...Needle and Ball; ...Heading indicator; ...IFR Flying; ...Straight and Level; ...Rate turns; …IFR Steep Turns; ….Altitude Control; …Rate Altitude Changes; ..Airspeed Climbs; ...Airspeed Descents; ...Level Off; ...Compass; ...Visibility; ...Determining Visibility; …Part 91 Factors; ...Flight Visibility; ...Ground Visibility; ...Low Visibility IFR; ...Single Pilot IFR; …IFR Descent; …IFR to VFR Scud Running; ...Emergencies; ...What to Do; ...Why and How to Detect Instrument Failure; …Airspeed Indicator; …Vertical Speed Indicator; ...AI and HI Failure; ...Electric System Failure; ...Vacuum Failure; ...Pitot-Static Failure; ...System cross-check for Failure; ...Test of Judgment; …Checklists; …The 'Whys' of IFR Approach Crashes; …Avoiding IFR Approach Accidents; ...IFR Needles; ...Horizontal Situation Indicator; …IFR Facts without Instruments; …Physical Causes of Disorientation; …

 Gadget: K-mart altimeter bug

1/2" suction cup with straightened hook.

Turn coordinator vs Needle
AIM says that if radar contact is lost the pilot/aircraft must resume "normal position reporting". This means using the PTAEN mnemonic for position, time, altitude, ETA to next and name of fix that follows. Estimates should be based upon time but distance is o.k. as an add-on.

A proficient IFR pilot should be able to fly using partial panel to minimums in light turbulence. Needle/ball vs turn coordinator. The turn coordinator is not as good as the needle in showing a turn or wings level since it shows wings level before the wings are level. A pilot may make several tries before getting wings level when using the turn-coordinator. The needle 'senses' the turn

Attitude Indicator
The attitude indicator gives instantaneous indication of pitch and bank. It is the only instrument on the panel that provides a clear picture of the flight attitude of the aircraft. Most modern AIs permit full 360-degree rotation about the roll axis with pitch stops at 60 degrees. Marked to show + 50 degrees nose up/down and 20 degrees when inverted. but no specific degrees by markings. Do not have caging knobs.

The attitude indicator (called the artificial horizon in former years) has a vertical gyro as its spin axis. They do precess but it has an erection system activated by gravity that resets it back to the vertical. The AI has bank markings up to 90 degree banks. The first thirty degrees is divided into 10 degree units. Very close to the standard rate turns can be achieved by reference to the AI. Every airspeed has a degree of bank (coordinated) for a standard rate level turn; this is about 15% of airspeed; 15 degrees at 100 kts, 12 degrees at 90 knots. Use turn coordinator with ball centered to confirm angle required.

A Navy study found that during major attitude changes 85% of experienced IFR pilots focused on the AI. When the AI is set for level flight its movement can be set to position the nose for any selected climb speed. There will be a consistent correlation between power, trim, nose attitude and AI attitude. Knowing this removes the aircraft as a problem.

Instrument interpretation means to look at the instrument and make an appropriate correction for the indication. Instruments in a given flight condition are selected for pitch, bank and power. You set the aircraft attitude and power to get the trend you want. You fine tune using the instruments with numbers. Begin any maneuver using the attitude indicator (AI). Set the AI, check the trend of climb, descent, level, and turn. Now go to the numbers for making the selected flight condition precise.

Ability to scan from the Set AI to check the trend to the numbers back to the set requires prior knowledge of where you are going to move your eyes. In level flight, with a predetermined power and airspeed, the scan can be a relative easy and slow AI, HI, AI, Alt, AI. The scan must be changed and accelerated if a change of heading is required and even more speed if a descending turn is called for. The sequence of required instrument scan is not so important as keeping the eyes moving always back to the AI

Use the AI as the central instrument. It gives direct indication of pitch and bank information. It is the best single source of aircraft attitude. Flying the AI makes you safe. Make your turns with AI, check TC for accuracy, the VSI for perfection and use the HI (numbers) to measure results. Scan should include the AI in every second or third fixation. (You can't see when your eye is moving.)

The AI gives pitch attitude, bank attitude and bank angle

Attitude Indicator Errors
The erecting mechanism operates continuously but is limited to 3 degrees per minute to avoid errors due to sensed 'gravity' during banks. During prolonged banks in one direction this error can be significant. Very shallow bank turns or flying out of rudder trim for long periods can produce errors. Any maneuver that displaces straight and level will result in AI error if it lasts long enough. Coordinated and uncoordinated turns will do this. It is for this reason that holding patterns have the one-minute level flight legs after each minute of turn. This leg allows the AI to settle itself. This may be the reason the FAA prefers the 45/180 for the procedure turn.

When making a 180 degree steep turn and then rolling out your attitude indicator will show a nose up and wing down in a direction opposite the turn. The error is inherent to the erecting mechanism. The errors tend to cancel in 360 degrees. Taxiing turns are always skidding turns. It is normal for the AI to show up to five degrees of tilt during taxi turns. Any more requires investigation. AI gyrations during initial start of the engine is normal. If the bar fails to stay horizontal or tips over 5 degrees during taxi, it must be deemed unreliable.

A vacuum powered attitude indicator gives warning of failure. It will be slow to erect and may go through gyrations while erecting. It may be sluggish in flight. To see what an instrument does when it loses power--when the vacuum pump fails, for example--watch it run down after shutdown. There is no way to predict what an instrument with an internal problem will do. Don't chance flying IFR with an instrument that has failed and then recovered. Don't fly with one that is even suspected of being faulty. Being on partial panel (real failure) in IMC requires landing at the nearest suitable airport. Report failure to ATC. Airports with ASR approaches can give no-gyro approaches. On final, turns should be at half-standard rate. If controller offers no-gyro approach take it.

The AI and TC operate on vacuum and electricity respectively. If the information is conflicting (you know the standard rate reading of the AI for the different airspeeds) suspect one system has failed. Go immediately to the Compass as a friend you can trust.

Pitch
AI-
Airspeed and VSI (VSI shows vertical trend after a few seconds)
Altimeter (FAA primary-with the numbers)
Bank
AI
TC gives roll into turn rate, turn rate and coordination
HI (FAA primary-with the numbers)
Power
RPM
Airspeed indicator-with the numbers

AI Demonstration
Cover everything but AI (Simulates instrument failure of aircraft with (HSI) and intercept an airway or VOR radial in level flight. Fly radial using only AI.

Cover everything but AI and establish best rate pitch attitude going into successive left and right banks and then to one bar descent with left and right banks. Success depends upon power settings and changes.

Cover everything but AI and make timed turn to heading using knowledge of airspeed/angle of bank as function of turn rate. At the end of each timed turn check altimeter. Practice until you can make timed turns without changing altitude using only AI and your ability to fly aircraft.

Cover everything but AI and make timed climbs and descents using a set sequence of attitude, power and trim. Before recovery make a Check (peek) of VSI and altimeter to see how your settings are performing.

Turn Coordinator
The turn coordinator is usually an electrically driven gyroscope. It is mounted at an angle of 30 degrees with the back slanted downward. It is dampened to reduce the reaction to turbulence. It originally served to control single axis autopilot's. It senses both yaw mostly and roll rate slightly. Initially it senses roll and when the bank is established it senses yaw (rudder) input. Knowing the airspeed, the angle of bank can be inferred. The TC ball (slip-skid) indicator is smaller than that on the older needle and ball instrument. The TC will indicate the direction of a spin so you will know which rudder application is opposite. This is not true if the spin is inverted. In an inverted spin the turn coordinator will give incorrect information for recovery. A failed TC will "park" level. A very good reason not to use as a level flight indicator except in emergency.

Overhaul calibration of both TC and Needle is done by adjusting centering springs. As the springs weaken with age sensitivity to yaw increases so does gyro friction increase with age with a decrease in sensitivity. The net effect of these changes are unpredictable. Ground check of T.C. operation is that in a left turn the ball moves to the right and aircraft remains level.

Needle and Ball
The needle's gyro axis is mounted horizontally and spins up and away from the pilot. It tilts on the roll axis up to 45 degrees. It cannot move on the vertical axis. A yaw of the aircraft causes the gyro to yaw in the opposite direction. Reversing linkage gives correct direction and amount. Oscillations are prevented by a dashpot mechanism.

Heading indicator
Use 45 degree markers on heading indicator to fly 45 degree intercepts to airways and 45 degree holding pattern entries. Common procedure is to only set HI in level unaccelerated flight. Setting the HI should be part of every instrument approach checklist but especially the NDB approaches.

IFR Flying
A single instrument usually provides the best information for a maneuver. The use of secondary instruments is a MUST to provide the required redundancy to verify the validity of the primary instrument. The eyes must flick stop and flick from instrument to instrument. Any references to charts of paper should not exceed 3-seconds. Learn to improvise and deal with what you have where you have it. Control changes are made by finger pressure. IFR control input is by pressure not movement.

Straight and Level
Bank Pitch Power
HI, AT, TC AI, Alt, VSI Controls airspeed
If power is not not a variable then airspeed indicator is a pitch control.
Practice
Changing speed from cruise, to low cruise, to slow flight, full flap slow flight and back again while maintaining headings and altitude.

Rate turns
Bank Pitch Power
AI then TC, AI VSI, altimeter, AI Constant airspeed with throttle.
Practice
Cover AI for and HI well into exercise and use clock and compass to make variety of turns up to 360 degrees. Compass headings of 180 will allow you to keep wings level.

Advice
There are subtle difference in making airspeed maneuvers. If you are fast, slow or just right in level flight make power raise or lower the nose for you. Trim after the attitude/airspeed is acquired. Leveling off is done by 10% of the climb rate or descent rate.

IFR Steep Turns
Practice with both full and partial panel
--Roll into steep turn
--Use VSI for pitch because of its sensitivity
--Altimeter lag will make holding pitch/altitude more difficult.
--Lock arm and elbow
--Increase power as needed
--Rollout requires immediate forward pressure and rudder application
--Advanced practice would be doing 360s or 720s linked in both left and right turns

Altitude Control
As with full panel instrument flight, partial panel flight requires that the pilot be able to fly using pitch, power, and trim in such a way that achieving and maintaining level flight can be done using known performance factors of the aircraft. Once flying the airplane is not part of the IFR problem then the pilot can use the instruments to achieve desired performance. Partial panel flight control can only be reached using the mind and eyes while interpreting instruments. The lighter the touch the better.

In level flight the altimeter is an indirect indication of pitch attitude being level. Any rate change in the altimeter up or down is an indirect indication of a climb or pitch attitude with constant power. The pilot must learn to interpret the rate of movement as an indicator of attitude. What we wish to achieve is slow movement caused by gentle changes. Any effort to react abruptly will result in over-control. The pitch change occurs immediately but the instruments have delayed reactions. Always make pitch changes slowly and smoothly. These will get the plane where you want it with positive control. Your reaction to an altitude deviation should be a slight change in pressure designed to slow down the needle movement. If the needle reacts abruptly too much pressure has been used. The slower the needle moves the closer the aircraft is to the desired attitude.

Using the vertical speed indicator as a direct indicator of pitch attitude can lead to abrupt over-control or chasing of the needle. This is a most common student error since the VSI needle tends to be quite active. The VSI is a trend as well as a rate instrument. Once again, only very light control pressures can be used successfully to stabilize the VSI.

Rate Altitude Changes
Climb
--In straight and level change to climb ias
--Use power to get 500 fpm climb
--Adjust pitch for airspeed
--Primary for pitch is VSI
--Airspeed is primary for power
--Coordinate pitch and power for performance

Descent
--Reduce power for 500 fpm descent
--Adjust pitch for constant ias
--Ias is primary for pitch until VSI is 500 fpm descent
--VSI becomes primary pitch
--Power primary for airspeed
--Coordinate pitch and power for performance.

Airspeed Climbs
Constant power and airspeed. From cruise, raise nose, then power, then trim. Airspeed is primary pitch.

Airspeed Descents
Power for airspeed to make airspeed primary for airspeed. IAS and VSI for pitch.

Level Off
Altimeter for pitch, power for airspeed. (do not reduce power until reaching desired airspeed.

To fly well you must master these basic maneuvers. Though never written into the PTS there are several identical pilot control applications that coordinate pitch and power to achieve needed performance. Most control applications require that the pilot anticipate errors because the corrections required are apparent.
power for airspeed. (do not reduce power until reaching desired airspeed.

Compass
The compass is the least likely to fail and any change in its numbers would indicate the opposite direction of turn. If ever the turn coordinator disagrees with the attitude indicator use the compass to break the tie. Heading indicator as a vacuum partner with the attitude indicator is a biased juror.

This material is included in the VFR material but is repeated because of the partial panel requirements of the IFR PTS. Mounted on the face of an aircraft compass is a chart. This chart is a record of compass error called deviation. As a pilot of a particular aircraft you should copy this chart for use in navigational planning.

Many airports have an area set aside for a compass rose. This rose is aligned using the variation between the True North and Magnetic North for this specific area. It shows the magnetic directions such as are used to align the airport runways. It is a place where aircraft are positioned and 'swung' through the various magnetic directions. This 'swinging of the compass' is done with all electric circuits functioning so that the operation of the compass will reflect this fact.

As the aircraft is positioned on the eight magnetic courses a small pair of adjustable magnets are moved so as to get the most accurate compass reading possible. As these adjustments are made, a record is made of the compass direction of the aircraft on the rose as compared with the best adjusted reading of the aircraft compass. This record is transcribed on to the deviation chart affixed to the compass.

In most cases this deviation is only one or two degrees. This exceeds the straight line flying ability of a pilot. However, with the advent of the Global Position System, it is becoming important to note deviation as a factor in navigation beyond the Practical Test Standards or the FAA written.

The numbers on the compass are opposite in order and direction from the HI. The reversal of the two numbering systems requires us to be consciously aware of the difference. Setting the compass to the HI requires that we note the compass lubber line is between two numbers either centered or near one than the other. These two numbers are then located on the HI and the HI set to correspond. A usual student error is to make a mistake setting the compass.

Flying with the compass is quite different from using the directional gyro. The compass has several inherent errors relating to turn, speed and geographic latitude. The compass should only be "read" in level unaccelerated flight. It is best (easiest) to make compass turns using the turn coordinator and time. At 3 degrees a second a turn of two minutes is 360 degrees, one minute 180 degrees, 30 seconds 90 degrees and 10 seconds 30 degrees. A normal count of 1, 2, 3, (4) will be close to 10 degrees. On the ground a compass should only be checked while taxiing straight or when stopped at a known heading.

The swinging and dipping of the compass during a turn or acceleration due to changes in speed or direction is a physical phenomenon caused when the north seeking end of the compass dives toward the north magnetic pole. The higher the latitude the greater the dipping tendency. Turns from a northerly heading lag behind the turn; turns from a southerly heading lead the turn. When the card is banked the compass dips to the low side of the turn. ANDS is the mnemonic for acceleration errors. In a shallow 360 turn the compass is most accurate at 90 and 270 degrees. In a smooth turn from a south heading the rate shown on the compass exceeds that of the actual turn at a diminishing rate until at 90 or 270 degrees. See AC 61-27C pg. 44.

In the planning of a flight the use of the mnemonic "True virgins make dull company" gives the order true course, variation, magnetic course, deviation, compass course, wind, wind correction angle, to provide the compass heading required for the flight. In level unaccelerated flight the compass is unaffected by turning or acceleration errors. the compass is the self contained and independent means of determining flight direction.

Visibility
Visibility Defined::
FAR 91.175(c)(2) defines visibility prescribed for an approach.
FAR Part 1 defines both flight and ground visibility, and there Is a difference in the two meanings.

Determining Visibility
--Decide what you will look for before beginning the approach.
--Study the approach lighting and runway length.
--MALS lighting system is 1400’; MALSR is 2400’
--Learn to count runway lengths.

Part 91 VisibilityFactors
Part 91 takeoffs have no minimums but...
Part 91 landings have three prerequisites
1. Normal descent
2. Minimum visibility
3. Runway in sight

You cannot descend below DH or MDA unless you have minimum flight visibility required by the approach plate. This determination of minimum is done by the pilot. The IFR training program does not teach you how to determine visibility. Reliance on a 45 minute old ATIS is likely neither valid nor reliable. The most difficult phase of any approach in actual conditions is where the transition for instruments to visual actually occurs.

You will be at the decision height about an eighth of a mile before you should see a runway at ILS minimums of a half-mile. Seeing the runway before reaching decision height means you have the required visibility. Seeing the approach lights but not the runway allows you to continue but the missed is your best option. Knowing that each group of lights are 200’ apart gives you a handy distance reference to the runway. If you see all of the MALSR you have required visibility. Seeing all of a MALS system is less than a half-mile of visibility, go-around.

Flight Visibility:
Average forward horizontal distance, from the cockpit of an aircraft in flight, at which prominent unlighted objects may be see and identified by day and prominent lighted objects may be seen and identified at night. Flight visibility is determined by pilot. A pilot may not land an aircraft unless the flight visibility is as prescribed in the approach procedure.

Ground Visibility:
Prevailing horizontal visibility near the earth's surface as reported by an accredited observer. Reported ground visibility has no reflection on actual flight visibility. Landing and takeoff visibilities are ground-based measurements.

Visibility above the minimums is a two-way street. It makes the takeoff safer but does not, necessarily assure a safe landing. Regardless of conditions, planning and flexibility are the keys.

Low Visibility IFR
Zero/zero takeoffs are in themselves not particularly hazardous.

Its the ‘what-ifs’ related to engine failure on takeoff or having an immediate need for an alternate landing field that makes such takeoffs ill advised. A straight-ahead landing requires that you know what is there even though you can’t see. You must review and know the departure area to gain even some element of survival.

Low visibility takeoffs require that you maintain runway headings and low visibility landings require a minimum visibility. A Part 91 pilot can depart in zero/zero but must have visibility minimums and the runway environment in sight before descending below MDA or DH. What you hear on the ATIS is not controlling. It’s what you see.

Clouds or rain are most often as stated. Fog can be variable and change rapidly. If fog is a factor be prepared to go to an alternate. Use a second pilot to call outside the cockpit while the first pilot stays on the instruments. In single pilot operations the greatest hazard in such conditions is to let your sink rate increase while you are looking for an opportunity to dive for the runway. Don’t!

Single Pilot IFR
The IFR pilot can fly into IFR in three different ways. He can fly into unforecast conditions or into forecast conditions. Regardless of the planning some unforecast conditions are a probability to be either better or worse. The degrees of certainty of a forecast is still making an IFR flight a study in risk taking.

A pilot needs to interpret a weather briefing, ask appropriate questions and get the notams. Additionally, pilot must have the assurance, skills, knowledge, references, preparation and experience needed to avoid an accident. The aircraft must be IFR capable and the cockpit must contain the requisite charts and publications for the flight. Just having them may not be enough. Availability is an essential. I recently had a chart slip off my lap and slide under the back seat of the aircraft. I could not reach the chart by any normal means. I used a plotter and some gum that I had been chewing as an extension of my arm. It was still a difficult maneuver VFR and perhaps impossible in IMC.

Is single pilot IFR a risk taking exercise out of proportion to any possible needs? It certainly is if you succumb to those
pressures inside and outside that take you past any personally imposed minimums. It certainly is if you cannot or have not planned the flight with an escape route. It certainly is if your gut-feeling is that you are in over your head.

It is not possible to substitute IFR simulation for the experience of actual IFR conditions. Only actual conditions can give you the turbulence, precipitation, wind shear and lighting changes that can cause vertigo. Compounding these conditions will be ATC speed-talk, demands, clearances, inquiries, and requests for readback. Worst of all will be that the controllers who have concocted the clearance are not Talking the language of the controllers who direct traffic.

I admit to a weakness in my IFR instruction in that in simulated IFR I seldom make a full-stop landing. In actual conditions a high percentage of approaches result in full-stop landings. The transition from instrument to visual references in minimum visual conditions gets far too little practice. I intend to make a higher percentage of full stop landings and published missed approaches in the future. Training must include hours of actual and opportunities for the student to make real pilot in command decisions.

The purpose of IFR training is to produce a pilot who has sufficient skills and competence to fly IFR safely during the refining period that follows. This period used in retaining proficiency and the actual application of past training. This training rests of several basic but mandatory maneuvers.

The IFR pilot must have automatic control of the aircraft through coordinated turns, stalls and patterns. The fundamental skills of IFR are straight level flight, turns, airspeed climbs and descents, a light or hands-off yoke touch, and throttle movement. A weakness in any of these areas will compound any procedure problems. Early mastery of these basics will reduce training time in the long run. If you can't fly using the gauges without thinking about it, you won't have the ability to think about all the other things involved in navigation and communication.

Primary instruments are always the ones with the numbers. For straight and level it is the altimeter for pitch, the heading indicator for bank and the tachometer for power. When an airspeed is assigned then the ias is primary for power as the throttle is adjusted to maintain airspeed. Ability to maintain heading and altitude over a distance is a basic requirement.

The turn requires that the altimeter be used for pitch and the turn coordinator for bank. Tachometer is primary for power. As before, required airspeed is controlled by power adjustments. The TC should be calibrated by doing timed turns. The rate of turn is based on airspeed and angle of bank. Turn rate decreases with reduced angle of bank and an increase of airspeed. Standard rate turns can be figured by using 10% of your ias and adding five. Limit your angle of bank to the angle of small heading changes. Five degrees for five degrees. Use the standard 1/2 angle lead in rolling out to a heading.

Constant airspeed/power uses the airspeed for pitch, the HI or TC for bank, and tach for power. Lead altitude by 10% of your rate of climb or descent. A constant airspeed climb/descent while turning you decrease pitch with increase of bank angle. Airspeed will be constant but descent rate will increase and climb rate will decrease. Pitch, bank and power are all changed.

You can practice constant headings first by constant airspeed and them by constant altitude. The variables are made through power changes from full to idle. This requires great attention to the rudder, elevator and throttle coordination. For constant airspeed the hands move in opposite directions to get pitch and power. Initiate the climb until stabilized then set up the descent. Repeat until you can anticipate the coordination required to keep constant airspeed.

The constant altitude requires a sequenced movement of both hands in the same direction. This exercise will require trim adjustments. Power is changed from full to idle and back again. Rudder applications must be anticipated to hold constant heading. Using power go from full power and back to idle several times.

IFR Descent
Never make descent below DH or MDA unless you can see at least one of visual items required by FAR 91.175.

IFR to VFR Scud Running
Contrary to popular opinion, there are valid occasions where reliance on scud running skills will be both useful and successful. There are several criteria that determine both usefulness and success.
--Fly only into improving weather.
--Fly only in VERY familiar areas
--Know the Class G airspace rules for visibility and cloud clearance.
--Long distance scud running is not recommended.
--SVFR and contact approaches must be requested by the pilot.
--Know your limits.
--Not everywhere nor every time.

Emergencies
Don’t fly instruments unless you are current and proficient.
--ATC facility malfunctions are rare but happen due to lightning strike, phone line cuts, computer crashes and saturation of system.
--Aircrew problems such as repeated failure to execute approach, severe weather beyond crew competence, fuel and situational awareness
--Aircraft equipment failure, maintenance or capability
--Don't let a situation become dire before taking actions and know what to do ahead of time. Most dangerous inadvertent unusual attitude is the spiral dive with increasing airspeed:

What to do:
--Reduce power
--Level wings
--Level flight by watching altimeter.
--Greatest hazard is over control.

FAR 91.3 states: "In an in-flight emergency requiring immediate action, the pilot in command may deviate from any rule of this part to the extent required to meet that emergency." Two-way com failure is an emergency.

Why and How to Detect Instrument Failure:
Instrument failure is not always accompanied with a warning flag. As a part of your pre-approach briefing you should
crosscheck all instruments to assure proper operation of primary instruments. Failure to make a verbal approach briefing
makes such a crosscheck essentially impossible.

Airspeed indicator
--Airspeed drops or stays at zero with probable cause blockage in pitot tube
--Ice is most common cause. If weather has been cold enough to freeze water, turn on pitot heat during preflight. --Failure to remove pitot cover is an embarrassing possible.
--If blockage includes some indication of airspeed, the indicator reacts as an altimeter. An increase in altitude causes an increase in airspeed. Descents decrease airspeed.

Vertical Speed indicator
--VSI not working
--Cause is blockage at static port
Solution is use of alternate air or break VSI instrument glass
1. Airspeed will indicate higher than actual
2. Altimeter will indicate higher than actual
3. VSI will show false climb

Attitude Indicator and Heading Indicator Failure. Suction gauge zero.
--Cause is failure of suction pump
Solution is to go to back-up suctions or cover instruments.
--Airspeed indicator will act as pitch indicator
--Turn coordinator for bank info.
--Compass for heading

Electric System Failure
Safe IFR flight is possible following an electrical system failure with only the pitot-static and vacuum instruments. Electrical systems usually fail slowly if the problem is in the alternator. Reduce electrical load to save battery. X-ponder only is good option. Radios on only for assistance. No nav radios if being vectored. Know where nearest VFR lies and head that way. ATC will provide traffic separation.

Vacuum Failure
Note: On average only one accident a year occurs solely due to vacuum pump failure where the pilot detected the failure and flew for nearly an hour before task overload precipitated the accident. Keep your partial panel skills and cover failed instruments.

Early warning of vacuum failure is the need to repeatedly reset the heading indicator. Vacuum systems tend to fail gradually. If the autopilot is coupled to the AI, the failure of vacuum pressure will cause autopilot to follow AI as it spins down until the autopilot's limits are exceeded. The inability of the pilot to detect this failure is believed to be the cause of many 'structural failure' accidents. The vacuum pressure gauge must be part of the scan.

If the vacuum pump fails, an electric turn coordinator and the pitot-static instruments provide sufficient information for safe instrument flight. An electric AI backup vacuum system is a worthwhile installation. See material on C-182 RG and it's vacuum back-up system.

Vacuum pumps fail because of contamination, heat and age. Pumps are usually flown until failure but a lead-in clue is no pressure at idle. The operation of the engine driven pump is to suck air across the instrument gyro wheels and exhaust it into the engine compartment. The intake air comes from the cockpit through a filter.

Of the three systems subject to failure, only the vacuum pump is normally flown until it fails. Fly long enough and you will experience vacuum pump failure. Given a choice vacuum pumps seem to prefer to fail in IFR conditions. A vacuum failure will cause the AI to indicate a slow turn where none was made or intended. The HI will begin to spin

Vacuum pumps die in several ways. The slow death occurs due to age, heat and contamination. Clean filter, good tubing and cooling will help prevent the slow death syndrome. Catastrophic failure is lack of internal lubrication. The gyro instruments will begin to spin down from their 17,000 rpm speed and the instrument will begin to tip or spin as the case may be. It is this gradual failure that causes loss of control. It is nothing like the sudden application of covers during simulated failures.

Pitot-Static Failure
In a thunderstorm pitot-static instruments (airspeed, altimeter, VSI) become unreliable due to radical pressure differences. The pitot heat should be part of the "actual" IFR checklist. Use pitot heat at first sign of visible moisture or loss of airspeed, expect high electric drain. Heavy rain/thunderstorm pressure changes may affect IAS accuracy. Pitot/static systems can be checked by use of alternate air. Breaking the VSI glass will cause reverse reading by the needle. Best sign of blocked static is constant altitude.

System cross-check for Failure
There are three mutually independent instruments that are available in IFR flight to correct bank. If one of the instruments differs from the other two, believe the two and cover the one. The AI, vacuum powered, is a bank (and pitch) instrument. The turn coordinator is electric. The compass is the third independent bank indicator. The failure of a single system only reduces the redundancy available to the pilot, not the capability.

Test of Judgment
--Advise ATC, request assistance
--Request vectors to best airport
--Request radar assisted approach
Vectors to final
Shallow intercept outside FAF
Surveillance and course deviation information

Checklists
Relying on memory to perform the required cockpit procedures is a relatively dangerous way to fly. Even the simplest aircraft will have over 100 specific steps required when progressing from preflight to tiedown. A complex aircraft may have eight times as many steps. All of these steps are as individualized as the aircraft and pilot.. The best way to develop such a checklist is to break the list into sections that can be counted on the fingers. Sections that can be designed to flow in sequence across, up or down the panel. You need sections that are systematically used in positioning and selecting cockpit switches and controls. The key to a flow checklist is doing the same thing in the same order every time. Only such a checklist can provide the maximum protection against interruptions and distractions.

Some situations do not lend themselves to checklists. Some numbers from the POH must be memorized and backed up in a readily available source such as the back of a lapboard. The PIREP, standard frequencies, airspeeds, that might have a memory failure under stress need to be quickly available. Any PTS checkride at any level either states or implies that the pilot must comply with use of the appropriate checklist at some point in every procedure. The pilot can make the choice of before, during, or after in fulfilling this compliance.

Other situations do lend themselves to short term memory use. In IFR approaches, having studied the approach charts shortly before beginning the approach can enhance the ability to recall essential altitudes, distances, radials, frequencies and procedures. Ability to do this allows more time on the gauges and control input. Most essential input into short term memory is the factors mentioned above as they apply to the missed approach. If a communicator is unclear it is best to re-enforce your memory bank by having the message repeated. Finally, short term memory works best if exercised.

Once the entire approach procedure has been reviewed and always in the same manner, there is no need to feel under extreme time/procedure pressure to get everything done. Excess pressure or quickness can cause the wrong thing to be done at the wrong time and in the wrong order. A pilot who has the basic ability to perform an approach sequence my fall into the dual traps of divided attention and limited time. These weaknesses are usually due to poor habits and reduced management skills. Basic to overcoming this weakness is the ability to say to yourself that a particular task can wait until later.

Successful approach task management means that you do the major 'killer' items at exactly the same place during the procedure.

Knowing that you have already made a complete approach review means that you know that the order of things can be accomplished one at a time. When you change to fullest tank, when you lower gear, when you adjust the propeller, when you go to approach speed are fixed elements of the procedure. Co-tasks such as the FAF and starting timer clock are always in sequence and before step down descent. Good cock,pit management is more a matter of attitude than it is of technique. Your attitude should include the requirement of never looking away from the instruments for over three seconds no matter how many times you make the switch. Identing needs to be done but not right away.

At some point in your training you begin to filter the various differences of performance and procedure from various sources and come up with your own way of doing thing. This is an important phase of learning and flying. We have sorted out what we have learned and settled on a preferred way of doing things. Some of these items are requirements, such as changes in radio or clearing the runway procedures. Some are optional procedures as for when to reduce power, use the fuel pump, or C.H. Lastly there are invariable elements of flying such as clearing for turns which have not alternate acceptable options.

The 'whys' of IFR Approach Crashes:
--Distractions
--Breakdown in situational awareness
--Unstabilized approach
--Inexperience with conditions

Avoiding IFR Approach Accidents
Talking to any ATC facility is not a guarantee of defense against your having a mid-air. Even IFR-VFR separation is
guaranteed only in Class A, B, or C. Most mid-airs occur at low altitudes near uncontrolled airports because that's where
the airplanes are. Aircraft shadows are your best indicator of low level proximity. Watch the ground. As with cars there
are built in aircraft blind spots that can only be uncovered by S-turns, head nodding, and a modicum of luck. Always check
the airspace you are about to enter.

--Use standard approach procedures
--Fly the procedure
--Have personal limits of visibility
--Have personal limits of pilot and aircraft ability
--Consider the missed as an always available option
--Have deviation parameters for executing the missed
--Have flight path and speed deviation limits for missed
--Have personal limits for a stabilized approach
--Be clear and understanding in communications
--Beware night and runway contamination
--Know your personal altitude AGL limits
--Go in knowing the numbers
--Share what you are finding out and doing.
--Recognize any inappropriate use of power
--Practice recognition of unusual attitude problems
--Recognize excessive and uncontrolled descent rates
--Configure aircraft for low speed operation
--Learn to recognize lack of preparedness
--Establish mutual understanding between ATC and pilot.
--Expect night, visibility and weather contamination of references
--Use Radar/GPS altimeter

IFR Needles
The best of approaches is the ILS since it gets you within 200' of the runway. The diagrams do not fully state the margins
shown to you by the needles. The following figures are generalizations that do not apply to all ILS situations.
1. At the marker (5- miles out)a one-dot localizer deflection equals 300 feet.
2. At the middle marker (1/2 mile out) a one-dot deflection equals 100 feet.

The glide slope is even more sensitive.
1. At the marker a one-dot deflection equals 50 feet of altitude.
2. At the middle marker a one-dot deflection equals 8 feet of altitude.
3. The glide slope flares a wingspan above the runway.

The non-precision approaches have minimums in the 500' range that usually means a low IFR condition will not allow the
runway environment to be seen.

Horizontal Situation Indicator

--Functions as VOR, ILS and heading indicator
--Reverse sensing is eliminated
Nomenclature
--Lubber line serves as heading index
--Course Deviation Indicator (CDI) gives course flown
--To/From flag and needle points parallel the to or from without reverse sensing
--Miniature aircraft gives visual angle of heading and course flown
--Glide slope usually on both sides of instrument
--HSI can be set to give direct indication of back-course approaches

IFR Facts without Instruments
--You can lose orientation in less than 20 seconds
--You can be upside down and not know it
--Your inner ear can be giving false information
--No pilot can fly in IFR conditions without visual reference

Physical Causes of Disorientation
--The inner ear is a three-axis gyro that require visual input to maintain spatial orientation
--The inner ear reacts to rate changes, not sustained change
--The inner ear will falsely interpret rate and non-rate changes without visual references
--The inner ear may not be 'triggered' by smooth trasitions in attitude on any axis
--Knowing how to fly instruments is no assurance that you are competent to 'trust' your instruments

Return to Whittsflying
Return to IFR Contents
Continued on IFR Systems