Engine weirdness on 767 immediately after takeoff

[InsanelyOne]

Last Saturday I was on an AA flight from Miami to Port-of-Spain on a 767-200. Let me first preface this with the fact that I'm a very seasoned flyer. Been traveling full-time on business for over 15 years and have flown thousands of flights. I've never experienced anything like this before. About a minute after takeoff (we had just passed over Miami beach and were now over the water) the engines dropped down to what seemed like idle speed, similar to what happens when you take off around a noise abatement area. But this was unusual in that we were over water. Within seconds, the engines were back up full throttle. Seconds later, back down to idle. Then back full throttle. This went on for what seemed like a few minutes. Sometimes the engines would quickly cycle idle/full/idle/full/idle/full in a matter of just a few seconds. The whole plane was silent and everyone was looking pretty scared. At one point, the engines stayed at idle speed for quite a while. During this time, several dings from the captain and the red light when on over the galley. (I've experienced that once before when we had a landing gear failure on a 727). Finally, the engines were back on full thrust and everything appeared back to normal. No explanation from the crew. We continued on to Port-of-Spain with no incident.

Thoughts anyone. I really was scared for a few minutes there. Thought the engines were about to fail.

[orangehuggy]

Hi, probably there was a spurious or off-nominal indication for one of the engines in the cockpit and the flight deck crew were cycling the engines in order to ascertain proper functioning and response. The key here is that if there was a problem with an engine (in this event there was not as the flight continued) and the engine failed/was shut down it would only effect one (1) engine and the 767 is perfectly happy flying on the remaining engine back to a suitable airport. An airliner engine fails/is shut down in flight every day on average and 100% of those flights land safely.









(btw 500+ post on .com about 100 on .info, can't I get grandfathered in here or am I stuck being "junior"?)

[Verbal]

It was the Throttle Gremlins.

[EconomyClass]

Flight management system was waiting for that first cup of coffee to clear out the cobwebs.

[MCM]

Or air traffic control were being a P.I.T.A and giving 1000ft level offs, or changes in requested speed.

[gjokkel]

The exact same thing happened on Lufthansa LH455 SFO-FRA (B744) couple of years ago. Right after a normal takeoff the engines did the same thing. It was above San Bruno/Pacifica (densely populated area). The FA sitting in front of me facing backwards left her seat (pretty uncommon during takeoff) and was watching the engines intake with a worried face. She was reaching out to grab the phone, but after 4-5 idle/full throttle cycles she sat back. I was watching the SFO waterfront down there and trying to forget about the big whites in the water.
After this the 12 hr flight went uneventful, except in FRA the AC was parked outside in front of the maintenance hangar and we were transported by bus into the terminal.
According to my pilot friend this is a fairly common procedure when one of the engines have a transient (?) problem.

[HalcyonDays]

Personally, I think MCM is on the right track here. It's not uncommon in my experience on climb-outs from busy airports in busy terminal areas for aircraft to throttle back and/or level out once or more as they make their way up, round and through descending traffic. So I suspect air traffic control requirements are the likely reason.

[Vnav]

Personally, I think MCM is on the right track here.

I think he's right on track as well. At places where you have multiple airports with multiple arrival and departure routes these numerous 1000 foot stepclimbs are not uncommon (Miami, SanFrancisco, and New York are certainly places where you see this). Although I've never said it to ATC, if I'm going to get a series of 1000ft climbs, I'd rather just get held down level and given a much larger climb when he can work it out.

In any event, when this happens, the pilot can make it a lot less unnerving for the passengers if he comes out of VNAV and switches to Vert SPD with a nice gentle 1000fpm or so. This requires far less thrust resulting in fewer wild swings between full climb thrust and whatever it takes to do 250kts level. It also results in much shallower climbs and more gentle level offs. There are certainly downsides in climbing with VSPD in terms of speed protection, and some pilots are hesitant to use it, but there's a time and a plce for everything and there's no reason to simply blindly use VNAV because you've become an autothrottle/FMS cripple. Speaking of which, another solution is to simply turn the A/Ts off and fly the p;ane smoothly.

[3WE]

...I think he's right on track as well. At places where you have multiple airports with multiple arrival and departure routes these numerous 1000 foot stepclimbs are not uncommon...

I was going to ask how there could be so much congestion since Spain is East of Miami and there can't be very many airports out East of Miami in the Ocean, and that three or four flights from MIA to Puerto Rico last year had what felt like a "relatively continuous" climb outs...

...Of course, as you implied, maybe there are other dummies out there who grab the wheel thing and the lever things and use them to smoothly operate the plane.

But as I think about it more- it might be one of those "great circle" things where your departure route goes ~"Northeast" along with 10-zillion other planes going to the NE US????

Would that be the basic departure route for Spain?

[orangehuggy]

...

Would that be the basic departure route for Spain?

Um, he was flying to Trinidad...

[InsanelyOne]

I'm having a hard time buying the stepclimb theory. The change in engine speed was too frequent. Imagine your in a car and the driver is slamming his foot down on the accellerator and then lifting it off repeatedly for a couple of minutes. As I said before this was like nothing I've ever experienced on a plane before. The engines behaved as though they had a mind of their own.
That said it was obviously nothing major as the pilot didn't turn back. Just me overreacting I guess.

[Thurian]

The exact same thing happened on Lufthansa LH455 SFO-FRA (B744) couple of years ago. Right after a normal takeoff the engines did the same thing. It was above San Bruno/Pacifica (densely populated area). The FA sitting in front of me facing backwards left her seat (pretty uncommon during takeoff) and was watching the engines intake with a worried face. She was reaching out to grab the phone, but after 4-5 idle/full throttle cycles she sat back. I was watching the SFO waterfront down there and trying to forget about the big whites in the water.
After this the 12 hr flight went uneventful, except in FRA the AC was parked outside in front of the maintenance hangar and we were transported by bus into the terminal.
According to my pilot friend this is a fairly common procedure when one of the engines have a transient (?) problem.

I think if the A/C had "gone in" I reckon the "Big Whites" (Great Whites?) would have been the least of your problems!

[3WE]

I'm having a hard time buying the stepclimb theory. The change in engine speed was too frequent. Imagine your in a car and the driver is slamming his foot down on the accellerator and then lifting it off repeatedly for a couple of minutes. As I said before this was like nothing I've ever experienced on a plane before. The engines behaved as though they had a mind of their own.
That said it was obviously nothing major as the pilot didn't turn back. Just me overreacting I guess.

Thanks to United Airlines (and their ATC channel) and Corporate Airlines and thier open curtains on J-31's, I can testify to what I think is a strong tendency of ATC to assign the new altitude right when you reach the assigned alititude.

If you pay attention, you can notice this tendency just riding in the back.....I can't count the level-offs that are immediately followed by more climbing or descending.

And, I think it's simple human nature. The pilot announces "leveling" and the controller looks up and realizes that the plane can climb (or descend) to the next level.

Of course we do need to credit the OP a little......He says he has lots of hours riding airplanes....and if he's a knowledgeable aviation enthusiast- he may be accurate that this was extra unusual.

[Gabriel]

Unless the step climb was in 200ft increments, this doesn't seem to match:

Sometimes the engines would quickly cycle idle/full/idle/full/idle/full in a matter of just a few seconds.

Also against the step climb theory, the witness doesn't complain of the roller-coaster effect (cycles of Gs above and below 1) that would result from changing from 0 to 3000fpm and back to zero so frequently (and hence so suddenly)

Either it wasn't a step climb, or the fingers of both hands are not enough to count those "few seconds".

[MCM]

If the change in engine speed was that frequent, then it wasn't going to idle. From your first post,

Sometimes the engines would quickly cycle idle/full/idle/full/idle/full in a matter of just a few seconds

.

Its worth noting that the engine can't really do this... to go from Full to Idle to Full would take the best part of 15 seconds per cycle. To do what you describe, it is far more likely to be changing in the range from cruise power to climb thrust. And yes, it sure does sound like its going to idle... frightened more than a few passengers over the years that one!

I certainly wasn't there, and so I can't tell you for sure what it is, but there are a few "usual" options... the altitude level offs discussed before (although you say thats unlikely, it might have been the cause of one or two cycles), and the Auto Throttle system in the way it handles level offs or mode changes can also have the thrust changing with the pilot then quickly changing the mode again.

While they are my preferred options, I certainly wouldn't rule out others... and being there, you'd have the best chance of identifying it, so I certainly won't make any categorical statements! My money is on a combination of speed and altitude changes (or almost changes), especially with the vagrancies of the 767 Auto Throttle.

And don't worry Insanely One, I've been flying it for about 6 months and its still making noises that I haven't heard before... you get used to it after a while!