This article primarily targets general aviation pilots that operate aircraft with vacuum pump powered instruments. The reader will get to know the threats posed by an aircraft vacuum pump failure in visual meteorological conditions (VMC) and, more critically, during instrument meteorological conditions (IMC).
Introduction
In any given aircraft, there are many instruments that help the pilot fly under adverse weather conditions. Some of these instruments are powered by gyroscopes that are driven by air pressure. The system pressure (or rather the vacuum pressure) is provided by vacuum pump(s).
Modern general aviation aircraft are equipped with sufficient power sources to power their modern glass cockpit displays (albeit sometimes in an emergency or standby mode). However, in the rare case that the aircraft loses all of its power sources, there is a need for backup (standby) instruments to provide the pilot with enough information to safely land at a suitable airport – and these are often powered by a vacuum pump.
In this article, we’ll have a look at how vacuum pumps work, which instruments they are essential for, and whether it is problematic if the vacuum pump-driven instruments fail in flight under VMC and IMC.
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How Does A Vacuum Pump Work?
The vacuum pump is an engine-driven pump that sucks atmospheric air through the system. The air flows through filters and then directly into the inlet ports of the instruments that require the vacuum-supplied air pressure to function. There is a suction gauge fitted between the inlet and outlet ports of the instruments that helps determine the differential pressure.
The outlet ports of both gyroscope-driven instruments are connected to a vacuum regulator that regulates the flow of air. The air is then vented overboard via the outlet port under the cowling. Those seeking an in-depth understanding of the vacuum pump’s mechanism can find comprehensive insights at CFI Notebook.net.
Which Instruments Are Powered By the Vacuum Pump?
The vacuum pump powers air-driven gyro instruments, thereby providing an independent power source that ensures some instruments still work in the event of an electrical failure. They usually include the Directional Indicator (DI), and Artificial Horizon (AH) aka Attitude Indicator (AI).
Electrical instruments are the Turn Coordinator part of the Turn and Balance, with the Balance part being basically a spirit level that requires no external power. The ASI, ALT, and VSI are all pressure instruments that work as long as static and dynamic air pressure is available through the pitot tube and static port.
For comprehensive insights into the instruments powered by the vacuum pump, the MidContinent offers a detailed look.

“Like many components, vacuum/pressure pumps have a defined service life, measured in operating hours and/or years. Even if the pump is working well and shows no signs of failure, it’s not a bad idea to replace it prophylactically on a regular basis to guard against failure on a dark and stormy night.”
aviationsafetymagazine.com
How To Determine If The Vacuum Pump Is Faulty?
One way to determine if the vacuum pump is faulty or not, is to observe the artificial horizon after the engine startup procedure during your instrument taxi checks. Indicators of a faulty vacuum pump include;
- If the artificial horizon lags significantly in the leveling process, wobbles or topples (even after being manually caged and erected)
- The red low vacuum warning flags indicator is present (or low vacuum indicator switch or light illuminated)
- You do not have the required suction pressure on the vacuum gauge
- The vacuum powered gyro instruments such as turn coordinator or the artificial horizon fail the instrument taxi checks
If your aircraft instruments fail these checks, then they are clearly unserviceable or you have a vacuum failure.
You may not require an artificial horizon (or turn indicator or turn coordinator) depending on your category and type of flight (i.e. private day VFR), however, it is not recommended to go flying with any unserviceable instruments, and it is far safer to instead have it checked out by a qualified avionics technician rather than having the artificial horizon malfunction while flying in IMC.
Why does an aircraft vacuum pump fail
An aircraft vacuum pneumatic system can fail in many ways – for example;
- Hardened rubber hoses can crack causing a vacuum leak and causing decreasing vacuum suction readings (or a low vacuum indicator switch)
- Clogged filters (such as inlet filter or instrument filters being clogged by carbon dust) could restrict the vacuum pump sucking air
- Loose fittings
- Fluid contamination or oil residue from other aircraft systems (such as fluid leaks, engine oil, hydraulic fluid, engine wash fluids or even deicing fluids) causing a wet pump. Vacuum pumps are a dry pump that uses self-lubricating carbon vanes.
- Not using proper operation of the aircraft when manually handling or turning the prop – the internal components of the vacuum pump are designed to turn in only one direction, which is why airframe manufacturer guidelines recommend only turning the prop in the correct direction.
AviationSafetyMagazine has detailed info on how to determine a faulty vacuum pump.

Is it a problem if the vacuum pump fails during flight?
During day VFR flight, a vacuum pump failure isn’t that big of a problem at all if Visual Meteorological Conditions are maintained and visual navigation methods are followed. This is because external visual reference points are used as the sole means of maintaining attitude and direction.
Navigation over featureless terrain with no distant features available as a stable reference point (or IMC navigation) requires more reliance on the AH, and DI/DG or compass. If a vacuum pump failure occurs in IMC – Instrument Meteorological Conditions, it’s only a problem insofar as flight using only the remaining instruments is required – limited or partial panel flying. Since vacuum pump failures don’t occur very often, especially while in IMC, it’s unlikely you’ll ever use limited panel instrument flying skills, but it’s wise to be prepared all the same.
This is why partial panel instrument flying is taught during pilot training. Generally, if you still are able to use a wing leveler or auto pilot coupled to an electrical powered gyro, this will greatly reduce your workload.
Normally, in VMC conditions it is very easy to spot a failure of the AH. The real problem that pilots face is a failure of the artificial horizon while in IMC. The failure is insidious and slow to set in thus luring the pilot into a false sensation that their aircraft is slowly banking whereas they are in level flight.
“Do vacuum pump failures cause accidents? The AOPA Air Safety Foundation found 40 accidents from 1983 through 1997 involving vacuum pumps. Thirteen listed a broken vacuum pump as the cause of the accident, while most listed the failed pump as one factor contributing to the accident, but not the only one.”
aopa.org/training-and-safety/students/flighttestprep/skills/vacuum-system-failure
Once it is established that the vacuum pump has indeed failed, it is best to back up any adjustment made to the controls using secondary sources such as turn and bank indicator, altimeter, and using senses such as hearing and sensing pressure changes etc.
A good technique to cope with vacuum pump instrument failures is to remember the mnemonic “Pitch + Power = Performance”. Basically, the concept being that if a pilot sets a particular pitch attitude and a particular power setting then he/she can attain a particular performance. This can be a useful reference guide especially when flying partial panel under IMC or when the workload is high.

Normally, the autopilot is not affected by aircraft vacuum pump failure but it is strongly recommended to disconnect the autopilot and fly manually if a vacuum pump failure has been positively identified.
For more information, AOPA has a good write up covering vacuum system failure.
Conclusion
Airline and military pilots seldom practice partial panel flying and approaches because modern airplanes have such a high level of redundancy built into them that the chances of reverting to standby instruments are very slim and negligible.
Although general aviation aircraft today are equipped with modern glass displays, general aviation aircraft are still equipped with a standby vacuum system and backup vacuum pump just in case the aircraft loses all sources of primary power. Hence, it is vital that general aviation pilots be proficient in the recognition and correct diagnosis of the symptoms of an aircraft vacuum pump failure.
This accident video highlights the dangers of aircraft vacuum pump failure.