[aftbit]

Depressurization happened around 17:12:33 PST but the aircraft continued to climb until 17:13:41 PST, and the autopilot was configured for 10k ft at 17:13:56 PST. Why did it take the pilots a full minute to begin an emergency descent after the failure? I would expect that the nature of the accident would be clear nearly immediately, at least in the need to descend the aircraft.

[michaelt]

According to the plane's "memory items" [1] in response to a cabin altitude warning or rapid depressurization, pilots must:

OXYGEN MASKS - DON

OXYGEN REGULATORS - Set to 100%

CREW COMMUNICATIONS - ESTABLISH

PRESSURIZATION MODE SELECTOR - MAN AC/MAN

OUTFLOW VALVE SWITCH - CLOSE

Hold in CLOSE until outflow Valve indicates fully closed

If Pressurization is Not Controllable

PASSENGER SIGNS - ON

PASSENGER OXYGEN SWITCH - ON

EMERGENCY DESCENT - ANNOUNCE

The pilot flying will advise the cabin crew, on PA system, of impending rapid descent. The pilot monitoring will advise ATC and obtain area altimeter setting.

PASSENGERS SIGN - ON

DESCENT - INITIATE

I do giggle a little at the thought of a door flying off, the air rushing out of the cabin, and the pilots responding by switching the seatbelt light on.

The plane was only at 16,000 feet when it lost its door and according to [2] you've got 20-30 minutes of 'useful consciousness' at such an altitude, even without your oxygen mask on. So there was no need for an abrupt dive.

[1] https://www.theairlinepilots.com/forumarchive/b737/b737memor... [2] https://skybrary.aero/articles/time-useful-consciousness

[rootusrootus]

A minute is a long time when you're sitting at your computer. But after the sudden depressurization, I imagine the pilot is focused first on making sure he has complete control of the airplane, assessing the situation, running checklists. Besides, 10K is just barely above the normal pressurization altitude anyway, it doesn't pose an immediate risk to the passengers that justifies just nosediving towards the ground. Especially given how much air traffic is at lower altitudes that close to PDX.

Edit: Re-reading, it was more like 16K feet when it popped, 10K is what ATC assigned them when requested. Still low enough not to be a critical emergency. Some people absolutely will get altitude sickness at that level, but it's likely to be mild. Many people climb mountains much taller.

[SoftTalker]

First and most importantly the pilots have to get their own oxygen masks on, if they delay this at all they will become hypoxic, unable to think clearly, then pass out, and then it's over for all on board.

[rootusrootus]

Agreed, this is definitely the first order of business. Similarly for passengers, always put your own mask on first before helping anyone else near you. Can't help if you pass out.

[sofixa]

See Helios Flight 522 for how that ends when the pilots don't realise what's going on and don't put on their oxygen masks.

[bombcar]

You follow the procedure because in an emergency you don't know what is going wrong.

Better to climb for a bit more as you get your oxygen mask on than to try to descend immediately and make some problem worse.

We know it was a door plug blowing out, but in the past it has been entire major sections of the airframe ripping off, in which case sudden extra stresses are not what you want.

[ogurechny]

Let's assume that they did change the course when they were sure they can do that.

Pilots can't look at the rear view mirror, and see the whole plane. Accident reports on engine malfunctions routinely mention that someone had to check their appearance through the passenger window, and relay that to the pilots. In case of a blast so severe that the door flies off, it is safer to assume the worst. Say, that part of the plane disintegrated because of sudden collision. In such conditions, indications on what works and what doesn't are probably really messy and unreliable, and there can be not enough means to control the plane properly. Lower the nose too much, and you might not be able to pull it up any more.

Pilots probably did checklists with one eye on the instruments to check that they were not losing speed, that angles were correct, autopilot inputs resulted in stable flying, and so on, and deduced that everything still worked. By that time, they were probably informed that the plane was seemingly intact, although with a hole in its side.

[bronco21016]

Step one is to put on the oxygen mask and establish communications. After the startle factor, the masks being put on, then declaring an emergency, a minute really isn’t that long.

[blantonl]

I would expect that the nature of the accident would be clear nearly immediately

Not really. The cockpit door was blown open, and the pilot's headsets were blown off. It was a pretty chaotic event, and when you are flying an airplane, you definitely don't want to figuratively "jerk the wheel" - you remain calm and start running checklists.

[throwworhtthrow]

You can't leave your assigned altitude/trajectory without coordinating with ATC. Otherwise you may collide with another plane, which would make a bad situation worse.

[mazugrin2]

Sure you can, and they likely did start descending before contacting ATC. But before they did any of that, they had to spend some time donning their oxygen masks and doing a few other "memory items" before then descending.

[michaelt]

In this instance the report explicitly says:-

> Both flight crew said they immediately donned their oxygen masks. They added that the flight deck door was blown open and that it was very noisy and difficult to communicate.

> The flight crew immediately contacted air traffic control (ATC), declared an emergency, and requested a lower altitude. The flight was assigned 10,000 ft. The captain said he then requested the rapid decompression checklist, and the FO executed the required checklist from the Quick Reference Handbook (QRH). As the FO completed the checklist, the captain flew the airplane as they coordinated with ATC to return to the PDX airport. The flight landed on runway 28L without further incident and taxied to the gate.

So in this particular instance, when the depressurisation happened at a comparatively low altitude, the pilots did get ATC clearance before descending.

[lisper]

In an emergency you can do anything you think is necessary to address it. Source: I’m a private pilot.

[zer0x4d]

You're conflating the right to do something with whether it is advisable to do something.

Sure, you are ~allowed~ to begin an immediate descent in an emergency, but it is not a good idea considering from the pilot's perspective, the bang is most likely an engine going out and altitude is always your friend in this condition.

[bink]

The person everyone is replying to stated:

> You can't leave your assigned altitude/trajectory without coordinating with ATC.

They didn't not say it was advisable, but heavily implied it was required.

[mrguyorama]

The rule is "Aviate, Navigate, Communicate".

In an emergency, caring about ATC is literally your lowest priority, in every case. It is ATC's job to notice a plane no longer under their control and route other aircraft safely around it. Your entire job is to do everything you can to prevent the death of anyone onboard, and playing ham radio is rarely the best way to do that.

[16bytes]

Aviate comes before navigate and communicate. The pilot in charge is ultimately responsible for the safety of the aircraft, not ATC.

[luizfzs]

Also, running checklists for specific types of emergencies.

[NordSteve]

Let's imagine you're the pilot, and you're super busy with an emergency. You also know that there are mountains to the east of the airport. You also have ATC on the radio and they know about all of the meaningful obstacles in your area. Asking for lower in this situation (rather than using your emergency authority) is exactly what you want to do.

Looking at the track, they descend to 10000' until they start their downwind to base turn. Once they start that turn, they get a lower altitude (looks like 7000') until they are established on final and can fly an approach.

[sigwinch28]

More altitude means more time to work the problem.

[engcoach]

Fast hands in the cockpit are scary. Pilots take their time in emergencies because rushing will take your birthday away

[bagels]

Clearance + they were probably putting on their masks, and other tasks.