The International Cessna^® 170 Association

InFO - Noise Attenuation Properties of Noise-Canceling Headsets
Notice Number: NOTC0738


The latest InFO is now available for download at:

http://www.faa.gov/other_visit/aviation ... all_infos/

SUBJECT:

Noise Attenuation Properties of Noise-Canceling Headsets

PURPOSE:

This InFO alerts operators, directors of operations (DOs), chief pilots, and flight crewmembers who may be using noise-canceling headsets of the potential for misdetection of audible alarms and other environmental sounds.

My own experience using LightSpeed 25K headsets is that they primarily reduce propeller noise only. This actually makes the engine and other inflight audible cues more distinguisable.
It is my opinion that the FAA concern is most likely related to more sophisticated aircraft that have multiple warning/notices such as landing gear, overspeed, environmental, and systems warnings that do not exist in our Cessna 170 aircraft. However, I posted this message so that you might evaluate your own aircraft, and whether or not you have avionics which offer low-fuel warnings, timers, waypoint arrival, etc. chimes and/or audible notices, and whether YOUR brand/model of ANC headset might mask those notices.

All - part of my primary training with students is to teach them to fly the first few minutes (or until cruise altitude) with the noise-cancelling feature turned off. I want them to have all the odds in their favor should something go awry, and often it's a subtle sound that indicates Mr. Murphy has involved himself in your flight.

I also teach students to turn it off for a minute an hour (or a minute every thirty minutes if they are 30-minute PA28 fuel-tank switchers) for the same reason.

This weekend I flew up the Yosemite Valley for the first time. Always wanted to make that trip. We were above the 2000' AGL restriction, but there are not a lot of gliding options during the turn-around-the-point at Half Dome. I had my Bose switched off from when I entered the rough terrain until we exited. If nothing else it made me feel a bit more comfortable for the "just in case". It's a stunning flight if you've never made it. It's one thing to see El Capitan from the ground. It's entirely something differently to look straight down the granite wall from above. Wow.

RT

I found the notice about attenuation properties quite uninformative. It would have helped a lot if the FAA had given some indication of what prompted them to issue it. Any clues about what we should be looking for?

I, too, find that I can hear more with the noise cancelling turned on. That's because the ANR only cancels the low frequencies, but without the drumming of prop and exhaust, you're more aware of the higher frequency noises. It's hard for me to imagine what kind of alarm or alert sound would be cancelled out by the ANR, but then, I've never flown any really big, complex aircraft.