# Airbus A320 "triangles" on wall & other topics **URL:** \ **Category:** Factual Questions\ **Created:** [May 12, 2010, 4:21pm UTC](https://boards.straightdope.com/t/airbus-a320-triangles-on-wall-other-topics/539185 "2010-05-12T16:21:22Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![butler1850](https://avatars.discourse-cdn.com/v4/letter/b/779978/32.png) [@butler1850](https://boards.straightdope.com/u/butler1850)\ **Post date:** [May 12, 2010, 4:21pm UTC](https://boards.straightdope.com/t/airbus-a320-triangles-on-wall-other-topics/539185/1 "2010-05-12T16:21:22Z")
During a recent flight on a Delta A320, my wife asked me about some odd markings on the wall. About 3 rows behind the aft over-wing exit, there was a triangle on the wall, it was in the same location on both sides of the aircraft. It seemed to line up more with the trailing edge control (flaps) than any central point on the wing. My speculation was some sort of a balance point, or “this is the middle row of the aircraft” indicator for the flight crew. Was I right? I’m still not sure about the “barking dog” sound (this is how the cabin attendant described it) during taxi. The attendant that I asked said it was the hydraulic systems pressurizing, but I’m not sure I believe him. I suspect it was the “just give an answer” answer. I’m usually really good about the sounds in an aircraft, and am fairly knowledgeable about aircraft operations (for a non-pilot airplane groupie), but understand the frustration that they probably feel. ---
**Author:** ![ElvisL1ves](https://avatars.discourse-cdn.com/v4/letter/e/5daacb/32.png) [@ElvisL1ves](https://boards.straightdope.com/u/ElvisL1ves)\ **Post date:** [May 12, 2010, 5:03pm UTC](https://boards.straightdope.com/t/airbus-a320-triangles-on-wall-other-topics/539185/2 "2010-05-12T17:03:47Z")
[The triangles](http://www.fromtheflightdeckbook.com/2010_01_01_archive.html) show the windows the crew is supposed to use to directly inspect the wings for ice and frost accumulation. Not sure what sound you mean, but it very well could be the hydraulic pumps and accumulators. “Barking” might mean grabbing brakes, though. ---
**Author:** ![El\_Kabong](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/el_kabong/32/496_2.png) [@El\_Kabong](https://boards.straightdope.com/u/El_Kabong)\ **Post date:** [May 12, 2010, 6:37pm UTC](https://boards.straightdope.com/t/airbus-a320-triangles-on-wall-other-topics/539185/3 "2010-05-12T18:37:29Z")
> [@butler1850](#): > > I’m still not sure about the “barking dog” sound (this is how the cabin attendant described it) during taxi. The attendant that I asked said it was the hydraulic systems pressurizing, but I’m not sure I believe him. I suspect it was the “just give an answer” answer. This has come up before. It is indeed associated with the hydraulic system, and is common to all A320 (and related series) Airbuses. Here’s an explanation: > **[Sawing Off The Wings: What’s That Sound Beneath The Plane?](https://www.science20.com/scientific_notation/sawing_off_the_wings_what_s_that_sound_beneath_the_plane)** > > As I was sitting patiently in Long Beach waiting to exit the plane and listening to that weird sawing sound that I hear every time I fly on an Airbus A320, I was wondering two things: 1) Why does it sound like Paul Bunyon is attacking my plane with a... ---
**Author:** ![butler1850](https://avatars.discourse-cdn.com/v4/letter/b/779978/32.png) [@butler1850](https://boards.straightdope.com/u/butler1850)\ **Post date:** [May 12, 2010, 9:03pm UTC](https://boards.straightdope.com/t/airbus-a320-triangles-on-wall-other-topics/539185/4 "2010-05-12T21:03:49Z")
Reason # 856 that I love the Dope. Both questions answered in a couple of hours. I’m sad that I was wrong on the triangle account, and happy that I got a real answer from the cabin crew! I tried for a half hour of searching in Google, and got nothing. My Google-fu must still be in Arizona on vacation! The sound is much easier to replicate with sound, than to type out “how it sounds.” 😃