Low flying jet due to door noise. What happened?

I was curious if any of our aviation industry members could satisfy my curiosity. On the flight I just took to SF the pilot announced we’d be flying low (I think 13000 feet) because the galley door was making a high pitches whistling noise such that the attendants couldn’t work there. I didn’t hear the noise myself as I was further up in the plane.

Anyway, we proceeded all the way to SF at the lower altitude which I suspect was the reason it took about 40 minutes longer than usual. The pilot assured us that the pressurization wasn’t compromised and that even if it were we could still breathe at that altitude so we’d just proceed to SF. Apparently when this happens it’s because “something got stuck in the door”.

So what exactly happened?

Until an actual aviation expert comes along I can offer some insights I’ve gleaned from many hours of aviation-related youtube videos.

It’s due to a couple of things.

  1. Professional pilots are trained to be very cautious when it comes to the safety of passengers and crew. They may have said pressurization wasn’t compromised, but that doesn’t mean there’s no leak, or that pressurization could fail at higher altitudes where the pressure differential is greater. Also, if the door problem suddenly gets worse they’re already at a safe altitude.

  2. I’m pretty sure there’s a regulation that they can’t go above a certain height if they aren’t absolutely sure the cabin is pressurized and can remain pressurized. Normally, they can trust the aircraft designers and engineers who said “this plane is safe up to so many feet”. However, when something isn’t working properly, they don’t know how high the plane can go safely.

Be glad it was just a longer flight. If they’d had to switch aircraft the delay would’ve been a lot longer than 40 minutes.

Since the question has been pretty much answered, Driver8, let me just add that the power lines have floaters so the airplanes won’t get snagged. :wink:

I assume this was a relatively short flight, yes? Not New York to San Fran? But yes, this was probably a limitation due to pressurization issues. Sounds like you flew with the plane un-pressurized.

The business jet I fly has a few scenarios where we would fly at a lower or intermediate altitude. One is if we are using only one of the two air “packs”. In that condition we can pressurize on the single pack, but have to fly at an intermediate altitude (I think the book calls for 25,000’ max) in case of a further loss requiring an emergency descent. The plane I flew at my last job had a limitation involving the secondary door seal, which sounds similar to the issue your flight experienced.

Take a break, Driver8. We can reach our destination.

It’s still a ways away, but to help get us there:

I’m not a pilot, but I am an aerospace engineer who’s worked on commercial aircraft. That said, there are many commercial pilots here; their practical/operational experience may override some of what I say below.

The whistling noise suggested that something was up with the door seal, but it was probably unclear exactly what the problem was. I’m betting that the pilot elected to stay around 10,000 feet because, in the unlikely event that the door seal suddenly blew out, the sudden decompression wouldn’t be a problem at that altitude. Sedentary but otherwise healthy people can breathe fine without supplemental oxygen at 10,000 feet.

(I once climbed five flights of stairs while wearing two backpacks—about 100 lbs in total—in La Paz, Bolivia, which is at about 13,000 feet. I had to stop every five steps or so, but I did it).

The pilot couldn’t know for sure what was causing the noise. It could be nothing of concern or it could signal imminent failure of the door. In that situation, The pilot had two options: turn around, land and have the ground crew check it out, or keep flying and hope he door seal held (which it probably would).

By flying so low, the pilot saved everyone a lot of hassle: the passengers got where they were going with minimal disruption and the airline had less of a delay to cascade to other flights. And if the door seal failed at that altitude, it wouldn’t be a big deal at all—the plane was already at an altitude that doesn’t require pressurization. (The pilot may well have dived to 10,000 feet anyway, but perhaps at a less urgent angle than under the same circumstances at a higher altitude).

IMHO, the pilot’s decision to continue to the destination at a low altitude was a pretty great compromise between safety and convenience.

Air is denser at low altitude, so flying so low burns more fuel than flying at, say, 33,000 feet. Even so, continuing at low altitude likely used significantly less fuel than turning around, landing and then taking off again after a repair. Just like in your car, going slower in a plane generally burns less fuel than going faster. So the extra 40 minutes could have been partly due to the pilot’s efforts to minimize the extra fuel burn from staying so low.

Plus, if the pilot maintained pressurization during your flight, flying at 13,000 feet puts a lot less stress on that possibly-failing door seal than flying at a traditional cruising altitude, making decompression even less likely. (The plane is pressurized to a level consistent with an altitude of about 8000 feet in either case, but the pressure differential the seal must withstand is a lot greater at cruising altitude).

As dstarfire said, this decision by the pilot minimized inconvenience and maximized safety for the passengers and airline alike. My answer repeated a fair amount of other posters’ points, but they were good points!

Even if a door seal blew out at 35,000 feet (again, exceedingly unlikely) sudden decompression at cruising altitude is relatively safe as emergencies go. The main risk is loss of consciousness due to hypoxia, which is really only a problem if it happens to both pilots. The pilots’ first order of business is to put on their oxygen masks and then dive aggressively to 10,000 feet. This ensures everyone will remain conscious even when the oxygen generators run out.

A passenger who didn’t put a mask on and passed out during a prompt dive to 10,000 feet would still be ok. They’d regain consciousness at some point during the descent, most likely with no ill effects.

Many remember when Southwest flight 1380 had a window blown out after an uncontained turbine failure threw debris against the fuselage. The passengers were losing their religion (and probably invoking it) partly because the pilot immediately entered a steep dive to 10,000 feet, as procedure demands.

I saw video from that flight in which passengers shouted things like “we’re all going to die,” but in hindsight, there wasn’t much actual danger. The aircraft was structurally sound and the pilot had the plane (and the situation) under control. But the passengers couldn’t know that at the time, and I’m sure the sense of panic was amplified by the fact that a woman was partially sucked out of the missing window and some passengers were trying to pull her back in. (Sadly, she died).

I’ve never been in a similar situation, but I can understand why a passenger without specialist knowledge would flip out. I’d like to think I’d remain calm, though I’d certainly be alarmed. But a steep dive doesn’t imply a loss of control under those circumstances. I’d be a lot more scared if we seemed to be spiraling or at an angle past vertical. (Passengers notoriously overestimate the severity of maneuvers…a 45-60-degree dive would be described as “vertical” by many. I’m sure I’d overestimate as well).

Again, I’m not a pilot, so I’d be grateful for any corrections and/or additional details.

ETA: I didn’t see Llama Llogophile’s post until after submitting mine. Oops!

Yes, it was Seattle to San Francisco. Normally just under two hours. It seemed to take roughly 45 minutes longer than usual due to this low altitude flying.

What people are saying matches the details. I imagine it really wasn’t about the noise but rather not having the attendants close to the door in case it failed.

I imagine they were trying to avoid more cascading delays. My original 9:10am flight was cancelled, this replacement flight was delayed 3-4 hours and only left around 3:30pm (after about an hour of waiting on the plane before de-icing and take off).

Thanks for the detailed responses.

It could still have been about the noise. Leaky door seals can be horribly noisy without being a problem in terms of pressurisation, and you find that it will happen at a certain altitude. It is possible that it happened exactly as you were told and that they just flew low to stop the noise.