Frontier Airlines' Squeaky Squeegee Sounds

Frontier planes with a few of their
cute animals (source)
I had never flown with Frontier Airlines—in fact I'd hardly even heard of them—until just a few months ago, when I flew from DC to Phoenix (through Denver) to spend Christmas with my girlfriend and her family in central Arizona. (Apparently, however, Frontier will no longer offer service to Phoenix in little over a month.) Just yesterday I flew Frontier again, going from DC to Denver and then from Denver to Fargo in order to spend my spring break with my girlfriend in Fargo-Moorhead. Overall I've really appreciated Frontier—their good service, (relatively) cheap prices, and the cute animal mascots they have. There's just been one weird experience, however, that I've had on all six of my Frontier flights: It's a very weird sound the airplane makes before takeoff and after landing, and I had never heard it anywhere else before.

a photo of mine from Denver
International Airport—Frontier's hub
To me, this sound the Frontier airplanes make before pushback or during taxiing is like the sound a squeegee makes on a car windshield—a quirky, squeaky noise. Some people describe the noise online as being like a dog barking, or a hacksaw, or just "plastic on metal," and it's really kind of humorous. On one of my flights I laughed about it with the person sitting next to me. (He had no idea what it was either.) It turns out the noise is perfectly normal, but it's only produced by the Airbus models A319 and A320, which coincidentally make up the majority of Frontier's fleet. Since I've mostly flown with Alaska Airlines all my life, which uses only Boeing 737s, and I've only been in an Airbus a few times before, I think my first flight with Frontier was the first time I'd been in an A319 or 320.

I personally know nothing about airplane mechanics, but it seems from the posts of enthusiasts and experts here and here (and in other threads and on other websites) that this squeaky squeegee "barking" sound is created by the Power Transfer Unit (PTU) when there is just one engine running. Since the PTU is located near the wing roots, it makes sense that I felt the sound was going on right underneath me on a few of my flights, when I sat next to the wings. And, since the noise only happens when one engine is running, it makes sense that it only occurs for brief periods of time during pushback or taxiing.

I'm glad I finally took the time to find out about this quirky noise and why I had only ever heard it on one airline. It turns out different models of airplane all have their quirks, and the Airbus A319 and A320s, like those used by Frontier Airlines, just happen to have PTUs that make silly squeaky squeegee sounds. I hope this post provides you with an answer to your gnawing question, or just a bit of amusement (or fair warning for the future). On Peter's Publisher, you never know what I'll write about next.