March 8, 2023. Pacific Plunge.
In mid-December, a United Airlines 777 descended rapidly towards the Pacific Ocean shortly after takeoff from Maui, Hawaii, coming less than a thousand feet from the water before safety climbing away again. The incident was under investigation by United and the FAA, but otherwise hadn’t garnered much attention. Then the media got wind of it, and now it’s everywhere.
To this point I’ve avoided any commentary or statements. The lack of hard info makes speculation and conjecture risky. Even in pilot circles little is known. But considering the level of hype this story is getting, I should probably say something. So here it is:
The rumor going around — again, it’s a rumor — is that the pilots went directly from flap setting 20 to flap setting zero (up) just after takeoff.
Normally, the flap and slat retraction sequence takes place in increments, as you accelerate during climb. Hitting a certain speed, the flying pilot calls for the next position. The monitoring pilot then verifies the correct speed and acceleration, and brings the flap lever to the proper setting.
The takeoff flap setting in a 777-200 can be 5, 15, or 20, depending on runway length, weight, and other factors. As a ballpark rule, the shorter the runway, the higher the setting. Less runway equals more flaps, in other words, to help the plane generate as much lift as possible in the shortest time.
Flaps 20 would be the expected setting for takeoff from Maui, where the runway is stubby. The plane would lift off at a relatively low speed, then accelerate through a series of “gates” during which the flaps are brought up in steps. Going straight from 20 to zero would suddenly leave the plane in severe danger of stalling. And if that’s what happened, we presume the “dive” toward the ocean was the crew’s attempt to gain speed and protect themselves from a stall. The correct move, in that circumstance. Perhaps the flaps were re-extended as well; we don’t know.
Indeed, we don’t really know anything. Whether things happened as described, I have no idea. This scenario — or some similar version of it — is certainly possible, but it’s hearsay at the moment. If things did occur as described, and the pilots bypassed the normal retraction sequence, the question is why. It surely wasn’t intentional. A misunderstood command, maybe, compounded by the second pilot’s failure to verify? Something like that?
Meanwhile, a different rumor describes a significantly different chain of events, this one involving an incorrectly set altitude window and subsequent VNAV mode activation… It gets technical; I won’t bore you with the details. From what I’ve been hearing, the investigators’ main focus is on a breakdown in crew coordination. What that means, exactly, remains to be seen. We’ll have the whole story eventually.
Photo courtesy of Unsplash
