Engine weirdness on 767 immediately after takeoff

[3WE]

...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)...

But neither does he mention strong acceleration and "deceleration"

With the power cycling like that you should sure be feeling some strong horizontal acceleration and likely deceleration if thrust is cycling from full to idle.

It is also worth mentioning that leveling off at low altitude (where there are speed resttrictions, and heck, likely ADDITIONAL a speed restrictions for being in-trail) is a very low power setting that sounds essentially like idle.

[Gabriel]

But neither does he mention strong acceleration and "deceleration"

With the power cycling like that you should sure be feeling some strong horizontal acceleration and likely deceleration if thrust is cycling from full to idle.

You're right

It is also worth mentioning that leveling off at low altitude (where there are speed resttrictions, and heck, likely ADDITIONAL a speed restrictions for being in-trail) is a very low power setting that sounds essentially like idle.

I "feel" that the vertical and horizontal accelerations would be clearly noticiable even if "full" is in fact "climb" and "iddle" is in fact "what it takes to hold 250".

[InsanelyOne]

But neither does he mention strong acceleration and "deceleration"

With the power cycling like that you should sure be feeling some strong horizontal acceleration and likely deceleration if thrust is cycling from full to idle.

It is also worth mentioning that leveling off at low altitude (where there are speed resttrictions, and heck, likely ADDITIONAL a speed restrictions for being in-trail) is a very low power setting that sounds essentially like idle.

I was definitely feeling acceleration and deceleration during this period. It did not feel like we were ascending however.

As I stated before, it obviously wasn't anything serious since we continued on our way with no incident. I was just trying to hear some theories as to what it could have been.

Many people are pointing toward a simple step climb explanation but that doesn't fit what I experienced. The engines were cycling rapidly between high and low thrust over and over and over and over and over in a matter of seconds. This was not a gradual thing. That's what made me alarmed.

[3WE]

...feeling...feel...rapidly...over and over and over and over and over... in a matter of seconds....not a gradual thing....

Ok, if you want much more help, you need to figure out the difference between objective and subjective terminology. Unfortunately, "a matter of seconds" and "not a gradual thing" means nothing.

So, think back, and try to remember the "one-thosand-one, one-thousand two" rule and then give us a number.

[TeeVee]

Seeing as how I fly out of MIA over one hundred times a year, I can attest to the fact that the events described are fairly common when departing MIA. It happens in MD-80's, 737's, Airbus A-300's, 777's, 757's, and as one more person knows, 767's. The only aircraft I have been on departing MIA that this has not occurred are ERJ's and ATR's. (yes, I only fly AA).

As for the lights, and the dings, on AA the dings represent certain phases of flight. For example, upon reaching 10k feet, the use of electronics is allowed. you will here one ding which will be followed by the FA's announcement welcoming you on board and telling you you can use electronics. insider tip for AA pax: if you do not hear the first ding after the first few minutes, you are almost certainly in for a rough climbout.

The different lights indicate calls from different extensions on the a/c. I do not know what color corresponds the flight deck on AA 767's but have posed the question to a friend that is a FA on AA. when she responds, i'll let y'all know. it could very well have been

As for the comment on how busy the airspace to the east of MIA is, remember, the OP stated she/he was headed to Port-of-Spain (i'm assuming POS, Trinindad) which is to the south-southeast of MIA. A typical takeoff route to the Caribbean if departing to the East is a very short flight eastward with a pretty early turn to the south. MIA is one of the busiest gateways to the Caribbean and points south so there is a pretty fair amount of traffic headed north, which ATC would have to consider in vectoring departing soutbound flights.

A final word on the "engines back to idle" comment, I too worried about this many, many years ago, but was quite correctly informed that if the engines were truly brought back to "idle" on departure/climbout, the a/c would lose altitude quite rapidly. In actuality, since your ears are, at that moment anyway, acclimated to the sound of takeoff power settings, just about any lower setting is quite noticeable. I'm certainly not a pilot nor am i knowledgeable about flying but i trust what pilot friends have told me and am pretty sure that the engines were not brought to idle, even if the crew were ordered to level off.

[TeeVee]

follow-up on lights

ok, heard back from the AA FA. i was wrong. there is only one light and it's red or orangish-red.

[Schorsch]

FLIGHT IDLE to MAX CLIMB takes about 3 to 6 seconds. Even if the actual engine noise might change substantially, it doesn't necessarily hit full IDLE.

Might it be some kind of turbulence? Autothrottle going wild trying to keep the airspeed? I would suspect some sort of Autothrottle issue. Otherwise, so if the engine seems unable to attain and hold a manually set N1/EPR/whatever, as pilot I would immediately return to the airport. A crappy Autothrust however can always be switched off.

I think the poor engine is not to blame.

[E-Diddy!]

Step climb sounds accurate. Remember a friggin huge CF6 turbofan engine is not your grandmothers riding lawnmower, when you advance the thrust levers (not throttles ) from a low thrust setting to a high thrust setting it takes several seconds for the engines to spool up to the higher thrust output.

[AndyToop]

I was definitely feeling acceleration and deceleration during this period. It did not feel like we were ascending however.

As I stated before, it obviously wasn't anything serious since we continued on our way with no incident. I was just trying to hear some theories as to what it could have been.

Many people are pointing toward a simple step climb explanation but that doesn't fit what I experienced. The engines were cycling rapidly between high and low thrust over and over and over and over and over in a matter of seconds. This was not a gradual thing. That's what made me alarmed.

on a 1500nm trip it wont have been anywhere near to max weight , so climb performance should have been really good. When the plane can easlilly climb at 4000+ ft per minute, then a 1000ft step will be measured "in a matter of seconds"

[Gabriel]

on a 1500nm trip it wont have been anywhere near to max weight , so climb performance should have been really good. When the plane can easlilly climb at 4000+ ft per minute, then a 1000ft step will be measured "in a matter of seconds"

He he he... you really don't know what it takes to make that, do you?

The simple fact that a plane has the performance to do a 4000fpm climb doesn't mean that you want to use all the performance available in a 1000ft stap climb.

Trying to do it smoothly, and starting from straight and level at say 2000ft, you can spend a couple of seconds moving the yoke back while the load factor increases to 1.2 Gs, then hold the 1.2Gs while the climb rate increases to 4000fpm, what takes another 10 seconds, then spend another 2 seconds slowly easing the Gs from 1.2 back to 1G, by then you'll have climbed to some 2400ft and you can give your passengers a 3 seconds brake climbing at a steady 4000fpm and a comfortable 1G until the plane has reached some 2600ft before you have to start to push down or you'll 3000ft, so you reverse what you've just done, you take two secons to slowly push the yoke and reduce the load factor to 0.8Gs, then hold the 0.8Gs for 10 seconds while the vertical speed reduces from 4000 to 0fpm, but spend the last two seconds smoothing the level-out and increasing the load factor from 0.8 Gs back to 1G.

Congratulations, you've just climbed 1000ft using a 4000fpm climb rate (for 3 seconds), but the whole maneuver took some 30 seconds (the rest of the time you've spent transitioning from 0fpm to 4000 and back to zero). Now go to the cabin and clean the vomit.

[3WE]

He he he... you really don't know what it takes to make that, do you...Now go to the cabin and clean the vomit.

Are you Flyboy5248m?

[Gabriel]

Are you Flyboy5248m?

Had I only said what you quoted, then yes I'd be Flyboy.

However, supporting what you quoted with what you didn't disqualifies me.

Yet, the addition of the Excel graph could qualify me as a valid Aavrakadabra (or something like that).

[InsanelyOne]

I just wanted to thank everyone for their input. I'm still not sure though what it is that I experienced. As I stated, I've been flying a LOT for business (since 1992) and have flown all over the world on virtually every kind of plane in existence. I've flown out of MIA probably more than 300 times alone. I understand that it takes an airplane engine time to fully cycle up so i can appreciate how my description of full/idle/full/idle sounds ignorant but I was trying to best describe what I was experiencing. I hate to belabor the point but I could almost describe it as a stutter. That's how quickly the perceived speed of the engine was changing (based on the pitch and volume of the engine noise). However during the entire episode it wasn't always so rapid a change. There were also less frequent increases and decreases in engine speed. It was very random. One thing I didn't mention. I was sitting on the left side of the plane in front of the wing. I was looking into the engine when this was happening and noticed what appeared to be a slight fluttering of light reflecting out of the engine. (I'm probably not describing that very well either). It was clear skies as well... no clouds or turbulence.

Thanks again for all that responded. This will be my last post on the subject as I think I'm starting to sound like Chicken Little.

[pothole]

I read this posting two days ago, and then experienced the exact same thing as One described while flying on YVR-FRA today.

Perhaps about 2 minutes after takeoff, both engines reduced power significantly. They stayed that way for about 5-10 seconds and then increased power again. After maybe 10 seconds at higher power setting, they reduced again to a lower setting. This cycle repeated maybe six times.

I also am a frequent flyer and have not noticed this previously. Sure the airplane stops climbing and holds at one or two different altitudes during the climbout phase, but this was different. The changes in acceleration that we could feel were much stronger in the horizontal direction than in the vertical. It felt like we were holding a constant altitude and the pilots were cycling the engines.

I wasn't a strong enough event to be "scary", but it definitely was "noticeable".

In this case the flight attendants who were directly in front of me did not stop chatting, so I guess nothing too serious.

If I had to bet on it, I would say there was some kind of transient problem that they were trying to clear before continuing the flight, which we did.

pothole

[Evan]

probably just stop and go traffic up there...

Does this have something to do with derated climb? I've read that some pilots actually brief pax before using climb 2 on the 767 because the thrust reduction is so noticeable it tends to scare them. Could switching between climb 1 and climb 2 produce this effect? With cost containment such an issue, I imagine derated climb is becoming more common SOP where available. Or perhaps the combination of step climb, derated thrust and VNAV? I don't claim to have any expert knowledge on derated operations, but I've also experienced something like this and would like to know what is behind it.