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Spatial Disorientation Accidents: IFR in IMC

SAFETY SPOTLIGHT: Spatial Disorientation

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An instrument rating is no guarantee of survival when instrument conditions prevail. It’s important to remember spatial disorientation can outmatch the most experienced pilots even in the absence of malfunctioning equipment. However, the high percentage of accidents caused by mechanical failures indicates a widespread inability to fly the aircraft by partial panel. Instrument-rated pilots are required to be proficient in partial panel flying, and these accidents indicate why.

It’s important to remember spatial disorientation can outmatch the most experienced pilots even in the absence of malfunctioning equipment.

No-Gyro Approach

During an IFR in VMC cross-country from Pontiac, Michigan, to Providence, Rhode Island, the pilot of a Mooney M20J was contacted by controllers and told he was “going the wrong way.” The pilot reported he had lost his vacuum system. ATC notified the pilot he would encounter IMC enroute, but the pilot elected to continue to his destination, about 180 miles away. During a no-gyro approach to the localizer in IMC, the pilot became spatially disoriented and reported to controllers, “We just lost it.” That was the last transmission from the aircraft. The resulting crash killed the pilot and his passenger. The dry air vacuum pump had been replaced about two years before and accumulated approximately 570 hours of use, under the manufacturer’s recommended replacement time of 700 hours or three years of service, whichever came first.

Inoperative Backup

After a late day business meeting, a pilot called flight service and requested an abbreviated briefing for a trip back to Oklahoma City from Duncan, Oklahoma. The weather briefer asked the pilot if he could go IFR. “I don’t want to but I guess I can if I have to,” the pilot responded. The briefer informed the pilot that IMC was moving toward the destination from the west. After the call, the pilot and his colleagues skipped dinner and went directly to the airport. At 2017, the pilot contacted ATC and reported he’d just left Duncan and was trying to maintain visual conditions. At 2019 he requested and IFR clearance. The instrument clearance was issued at 2020. At 2024, the pilot radioed ATC and said, “I have uh, a vacuum problem and uh panel situation here so I, I’m going to be a little limited on being able to talk to you.” Soon after, radio contact was lost. The C-182 crashed in an uncontrolled descent, killing the pilot and two passengers. Examination of the flight instruments found the gyro bearings for the turn and bank gyro were “heavily corroded and bore no evidence of recent rotation.”

Accident Case Study: Single Point Failure

A vacuum pump failure on a sunny day is no big deal, but in IMC—and especially without backup instrumentation—it’s a serious emergency. To see how a Bonanza pilot coped with that situation, and learn how you can do better, watch Accident Case Study: Single Point Failure.

Vacuum Failures

Instruments themselves can fail or the vacuum pump that powers them can fail. Indeed, vacuum pump failures are one of the most common squawks in general aviation aircraft. But pilots don’t train enough for this possibility, and the training they get is often inadequate. An instructor slaps a suction blinder on the attitude indicator (AI) and the directional gyro (DG) and says, “You just had a vacuum failure.” But in the real world, though the pump fails quickly, vacuum instruments themselves usually die slow deaths. The AI and DG – the two vacuum driven instruments – become more and more erroneous as the gyros slow their spinning and coast to a stop. The “No Gyro Approach” accident illustrates that fact. The reason the airplane was “going the wrong way” as reported by ATC, was because the pilot or autopilot was following the directional gyro. The pilot had ample time to divert but chose to continue. Even if you are skilled in partial panel flying, you won’t survive if your secondary flight instruments don’t work. In the second accident, evidence strongly suggests the turn and bank indicator was inoperative, as upon examination its gyro was heavily corroded and showed no signs of having worked recently. In other words, the instrument that would have been primary for maintaining directional control after a vacuum failure didn’t work. This put the pilot and his passengers in a virtually unsurvivable situation. 

Vacuum failures are hardest to notice in high workload environments, such as in IMC or immediately after takeoff. When a pilot finally realizes that various instruments aren’t in agreement, they must determine which ones are reading correctly and which aren’t. And once the problem is diagnosed, the pilot must be able to fly the aircraft without the instruments that are normally relied on most. That makes a vacuum failure in IMC, without a backup system, an emergency.

Tip: Practice instrument failures and partial panel approaches regularly.

Managing a Vacuum Failure

  • Most importantly, be proficient at partial panel flying. The time to practice is on a training flight or with a check pilot while you’re on your way somewhere, not when you’ve just had a vacuum failure.
  • Make sure the vacuum gauge is part of your scan, providing you with an early indication of a vacuum failure.
  • Have something available to cover inoperative instruments in the event of a failure. If you don’t have the covers used for partial panel flight training, keep some Post-it notes handy.
  • Make timed turns instead of using the magnetic compass to change headings.
  • Notify ATC of the situation.
  • Confirm the location of the nearest VFR weather.
  • Find out the conditions at the nearest airport with a precision approach.
  • Ask controllers for a “no-gyro approach,” so they can provide lateral guidance.
  • If available, select an airport with an Airport Surveillance Radar (ASR) approach

Real Pilot Story: Vacuum Failure in IMC

This Real Pilot Story shows how important it is to be proficient and prepared in the event of an instrument failure during flight in instrument meteorological conditions. As Dr. Donna Wilt can attest, practice flying partial panel in realistic situations, be resourceful, and know when to declare an emergency and use ATC’s help.

Tip: A “rate-based” autopilot gets its information from the electric turn coordinator, not the vacuum driven attitude indicator.videwatch