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ANR (Active Noise Reduction) headsets reduce the sound level to a pilot's ears by creating an interference wave that cancels out some of the environmental noise in the cabin. Some say that this reduces the pilot's ability to hear minor changes in the engine's sound, thus delaying the point when the pilot would take action to diagnose the problem or land the aircraft.

Are there any conditions of engine malfunction or suboptimal performance which a pilot wearing an ANR headset would not be able to detect, but one wearing a passive headset would?

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In summary, based on FAA/NTSB information it's possible in theory but no one really knows how individual headsets behave and there's no record of ANR headsets contributing to an accident.

First, according to a very short FAA information paper on Noise Attenuation Properties of Noise-Canceling Headsets, it's possible that they can mask important sounds:

While this technology can have many beneficial effects such as providing clearer communications, reduced pilot fatigue, and added comfort, electronic attenuation of important environmental sounds and alarms may occur

But the paper has no specific information or examples, and its only purpose seems to be to encourage operators to do their own testing (which is reasonable, since headsets can be very different):

Evaluations should be conducted while both on the ground and in flight during normal operating conditions to ascertain if any audible alarms or other environmental sounds, or combinations thereof, can be detected while electronic noise attenuation is on and active.

That paper is from 2007 and a letter of interpretation from the same year on headset requirements in part 121 operations implies that the FAA's main concern with ANR headsets is (or was) that the batteries run out and that might cause problems:

The FAA is particularly concerned, however, that Active Noise Reduction (ANR) headsets and headset adapters [...] that rely on battery power are subject to failure when [...] batteries discharge under normal use

And the FAA's general brochure on Hearing and Noise in Aviation mentions ANR headsets without any warnings or recommendations.

Finally, the NTSB's accident database has only one specific reference to an ANR headset (that I could find) and it explicitly ruled out any effect:

On January 5, 1998, the NTSB IIC used a Cessna 208B to determine if the Telex model ANR-4100 active noise reduction headset worn by the pilot at the time of the accident could have eliminated his ability to hear stall or fuel selector warning horns. All aural warnings were clearly audible with the engine operating and the headset active.

The information I found online on ANR headsets is overwhelmingly positive and I couldn't find any informal reports of pilots mishearing engine sounds either.

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  • $\begingroup$ well researched! Most 121 jet operators use single-ear headsets $\endgroup$
    – rbp
    Dec 22, 2014 at 15:53
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Although its possible to detect engine problems audibly, I don't think that's the primary mechanism (except for engine out) by which pilots are expected to detect engine anomalies. Part 91.205 requires that every aircraft be equipped with the following instrumentation, and these should be the primary mechanism by which engine malfunctions are detected.

(4) Tachometer for each engine.

(5) Oil pressure gauge for each engine using pressure system.

(6) Temperature gauge for each liquid-cooled engine.

(7) Oil temperature gauge for each air-cooled engine.

(8) Manifold pressure gauge for each altitude engine.

(9) Fuel gauge indicating the quantity of fuel in each tank.

That being said, ANR headsets attenuate sound, but don't eliminate it entirely. Having flown with an ANR headset for most of my flying career, I can certainly hear variations in engine noise in the mag check and prop exercise during the runup, as well as during throttle and prop changes. I can also hear a fouled plug during runup, as well as verifying it visually on the gauges.

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When talking about GA, if (for example) one spark plug goes bad, you can actually notice a difference when listening closely, and i doubt you could hear that with ANR! But one spark plug that goes bad during flight is not gonna kill you (well, hopefully anyways!). If there is a problem that will cause major power loss on the engine, you will definitely hear it! Other things like engine roughness, which is primarily as sign for lack of carburetor heat might not be heard though. Yet, when flying with a normal headset I find it hard to hear when the engines sound changes over some time anyways.

A ANR headset will reduce, but not limit your ability to hear the engine. It is a lot more comfortable during cruise though.

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  • $\begingroup$ I can certainly hear a fouled plug during run-up with an ANR headset. it may be because of the 250RPM drop in my airplane. if you are fouling plugs in flight, you need to lean $\endgroup$
    – rbp
    Dec 22, 2014 at 18:55
  • $\begingroup$ Yeah, during run up they are easy to identify, not only do you see and feel it whenever you go to a single magneto but you can clearly hear it as well. When this happens in the air though (happened twice to me already^^), it might be really hard with ANR as it is already hard with normal headsets. $\endgroup$
    – Maverick283
    Dec 22, 2014 at 23:08

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