Vacuum pump failure

If you’re training on a budget or simply appreciate old-fashioned steam gauges, you’re bound to run into some older aircraft with not-so-modern instrument panels. The attitude and heading indicators are often vacuum driven on these aircraft. Given the advent of modern flight decks with redundant systems, accidents caused by vacuum pump failures have become increasingly rare, but their rarity invites a deficiency in understanding and training.

In simple terms, the engine-driven vacuum pump in most GA airplanes draws in filtered air, creating suction, i.e., negative pressure, that actuates the aircraft’s gyroscopic instruments and enables the pilot to understand and measure their flight conditions (attitude relative to the horizon; direction; and turn coordination). Failure of this system leads to a loss of crucial flight information, and potentially, spatial disorientation. This is especially dangerous while flying in low-visibility conditions that require the pilot to rely solely on their instruments for reference, such as in instrument meteorological conditions (IMC) or during night flight over unlit or poorly lit terrain. It can be caused by contamination, mechanical failure, or improper installation.

1. Recognize there's an issue

The aircraft’s vacuum-powered gauges may become sluggish, slowly lose their functionality, and show progressively erroneous readings. An instrument cross-check can help you identify a potential problem. If installed, check your vacuum pressure gauge for a low or zero reading. Of course, if you have electrically powered backup instruments installed, now is the time to use them.


2. Aviate

Use the instruments you do have. This is where your partial-panel skills will come in handy. Maintain control of the aircraft using the altimeter, airspeed indicator, and vertical speed indicator. The turn coordinator, if electrically powered, can be used for rudimentary bank indications. It may also help to cover the failed instrument, perhaps with a sticky note, as the faulty indication can be distracting. If your autopilot isn’t dependent on a vacuum-driven turn coordinator, use it. Your GPS can help you maintain your heading and track. Avoid abrupt inputs to mitigate the effects of spatial disorientation.


3. Communicate

A vacuum pump failure in IMC is an emergency. Squawk 7700, contact ATC using “Mayday-Mayday-Mayday” to indicate distress, clearly state the issue, and follow the emergency procedures prescribed in your pilot operating handbook (POH). Keep in mind the controller may not know what a vacuum pump is, let alone the implications of its failure.


4. Navigate

Coordinate with ATC and determine the best course of action. Should you divert to the nearest airport with visual meteorological conditions (VMC)? Are you able to climb out of IMC and get to an airport in visual conditions farther away? As pilot in command, you are responsible for the safe outcome of the flight, and it is ultimately your judgment that will get you back on the ground safely. Don’t be afraid to say “unable” if ATC gives you instructions that you’re not able to safely comply with. You have a real-time understanding of what is happening in the air—they do not.