Question: Before pushback from the gate, I often hear what sounds like a drilling sound – short bursts, like an electric drill working against tension. Is it the cargo doors being secured, or something else?
– Peter Roth, Scottsdale, Arizona
Answer: You are probably hearing the electric motor that moves the cargo door. The door is raised and lowered by an electric motor on many airplanes.
Q: Why do Airbus planes make so much hydraulic noise before takeoff and after landing compared to Boeings?
– Peter Butler, Los Angeles
A: I suspect the sound you are referring to is the hydraulic system power transfer unit. The PTU makes a unique sound that has been described as “a dog barking,” “a NASCAR pneumatic tire gun” and “a grinding noise.” The PTU is active when one of the engine pumps is not producing hydraulic pressure. It may be active when taxiing on one engine before takeoff or after landing.
Q: What does the two-tone doorbell sound indicate?
– Larry S., Dayton, Ohio
A: It can indicate that the airplane is climbing above or descending below 10,000 feet. It can also indicate a request for an intercom call by one of the flight crew members.
Q: I am a very nervous flyer, and whenever I hear ANY sound on an airplane, I immediately think: “What’s that sound? Is it normal? What does it mean?” Most of the time I freak out, so could you tell me some of the sounds and what they mean/do?
A: My suggestion is to watch the flight attendants. They fly frequently and know what sounds are normal and abnormal. You have no reason to be concerned if the flight attendants are not.
There are many sounds in airplanes. The landing gear being retracted or extended can cause significant noise, the retraction or extension of the flaps can have hydraulic motor noise, and the extension of the flight spoilers causes buffeting and noise. All of these are normal sounds.
John Cox is a retired airline captain with US Airways and runs his own aviation safety consulting company, Safety Operating Systems.
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