Hey there!

It's been so long since I've posted on Airliners.net. I've been in the forums since around 1998, but not super-active as of recent. I have a question about the A350-1000 going from max thrust to climb thrust.

Recently I flew with Qatar Airways to Dubai. The DFW-DOH sectors were on an A350-1000, the DOH-DXB were on the A350-900. It was my first time on an A350-1000. On climb out from DFW, when the aircraft went from MAX to Climb thrust, the entire plane felt like it jerked, like when you pump the brakes to stop really quickly in a car. It was noticeably smoother on the A350-900.

I was curious as to why this was? It happened both times on the DFW-DOH-DFW legs, but not on any A359 flights I've been on.

Here's a video from the take off from DFW: https://www.youtube.com/watch?v=0NAHM2fJBgk

The switch happens around 1:17. You can actually see the camera move suddenly when it happens.

If the take off happens at high thrust due to runway performance requirements and a low climb thrust is selected (D2), the reduction in thrust can be quite large. Add to that the fact that some pilots are a bit more abrupt than others in pulling the levers back to the CLB detent after take off (and pushing the nose down if they're still hand flying at that stage) and you can get a slightly uncomfortable feeling in the back.

As Francoflier says, some pilots just jerk the thrust levers back to the CL detent when they see "LVR TO CLB". If the thrust difference is large, this can feel quite abrupt. A smoother movement will give a smoother thrust change. I personally don't see any reason to be rough on the controls.

You weren't necessarily at maximum (TOGA) thrust by the way. Most takeoffs are done with Flex (reduced) thrust.

777222LR wrote:

Hey there!

It's been so long since I've posted on Airliners.net. I've been in the forums since around 1998, but not super-active as of recent. I have a question about the A350-1000 going from max thrust to climb thrust.

Recently I flew with Qatar Airways to Dubai. The DFW-DOH sectors were on an A350-1000, the DOH-DXB were on the A350-900. It was my first time on an A350-1000. On climb out from DFW, when the aircraft went from MAX to Climb thrust, the entire plane felt like it jerked, like when you pump the brakes to stop really quickly in a car. It was noticeably smoother on the A350-900.

I was curious as to why this was? It happened both times on the DFW-DOH-DFW legs, but not on any A359 flights I've been on.

Here's a video from the take off from DFW: https://www.youtube.com/watch?v=0NAHM2fJBgk

The switch happens around 1:17. You can actually see the camera move suddenly when it happens.

More likely what has happened is your ears have played tricks on you. Sometimes the standard departure from airports has a relatively low level off segment, this is often to allow for other aircraft to cross above. When the aircraft levels off it can feel like deceleration, because you are level thrust comes back sometimes below climb thrust. They use the same technique in full flights simulators to provide the sensation of acceleration by tilting the bix the simulator is in.

More likely what has happened is your ears have played tricks on you. Sometimes the standard departure from airports has a relatively low level off segment, this is often to allow for other aircraft to cross above. When the aircraft levels off it can feel like deceleration, because you are level thrust comes back sometimes below climb thrust. They use the same technique in full flights simulators to provide the sensation of acceleration by tilting the bix the simulator is in.

No, this was not only audible, I felt it. I was in a rear facing business seat, and both times on the A350-1000 I was thrown into the back of my seat rather abruptly due to the quick deceleration. I've flown the A350-900 many times and this has never happened. This happened both on DFW-DOH and on DOH-DFW.

777222LR wrote:

No, this was not only audible, I felt it. I was in a rear facing business seat, and both times on the A350-1000 I was thrown into the back of my seat rather abruptly due to the quick deceleration. I've flown the A350-900 many times and this has never happened. This happened both on DFW-DOH and on DOH-DFW.

A relatively low level level off would explain that, climbing at 2000 fpm level off then reduce thrust as to not over speed.

zeke wrote:

777222LR wrote:

No, this was not only audible, I felt it. I was in a rear facing business seat, and both times on the A350-1000 I was thrown into the back of my seat rather abruptly due to the quick deceleration. I've flown the A350-900 many times and this has never happened. This happened both on DFW-DOH and on DOH-DFW.

A relatively low level level off would explain that, climbing at 2000 fpm level off then reduce thrust as to not over speed.

So we think it was a coincidence that the same feeling occurred taking off from Doha to DFW?

There also might be some effect from the difference of the massive fuel load (DFW-DOH) versus tiny fuel load (DOH-DXB). Just a thought. The difference would be around 200,000 lbs of dead weight.

I don't think so. The OP clearly states that the airliner deaccelerated on takeoff during both segments of DFW-DOH. This is ridicules of course because who the hell would do that!!!

Apparently shortly after takeoff the airliner reduced climb rate/thrust which would reduce the rate of acceleration. A reduction in acceleration is not deacceleration. That plus the fact that the OP was sitting backwards would explain his confusion.