saab2000
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Question for Airbus A330 pilots

Wed Mar 04, 2020 12:49 pm

I am a 737 pilot for a major US carrier but am quite unfamiliar with Airbus systems and only have a light knowledge of oceanic flying. I've done two crossings as a pilot but most of my career has been within Europe and within North America.

About a month ago I was coming back from ZRH to ORD on an A330-300 with LX. Fine experience on my former carrier though that is now a long time ago.

About an hour east of the southern tip of Greenland we began to encounter some quite strong winds and strong turbulence. Nothing severe but pretty good quality moderate. I wouldn't have wanted to be walking in the aisle at the time. This is nothing unusual of course but what really got my attention were the changes in the engine speed. This strong turbulence lasted at least an hour.

We began to hear the engines surge and spool back for 15 seconds or so, on and off, for minutes at a time. It was almost as if the airplane was experiencing fairly strong mountain waves even though we were hundreds of miles from any terrain. The engines seemed to apply full thrust for 5-15 seconds then spool back to a much lower setting, then re-spool to full thrust or nearly. As mentioned, this went on for a long time. We climbed from FL380 to FL390 but that didn't really do anything to help.

Finally, abeam the southern tip of Greenland, this turbulence and engine surging came to an end, rather rapidly.

Can anyone with transatlantic experience speak to this? Do mountain wave conditions exist from the terrain in Greenland? Also, how does the Airbus autothrust work regarding fluctuations in airspeed? The 737 autothrottle is OK but not fantastic, especially at high altitudes.

Just curious. I have no heavy jet experience and only very minimal oceanic experience.
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thepinkmachine
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Re: Question for Airbus A330 pilots

Wed Mar 04, 2020 2:34 pm

Hi! Used to fly the 330 across the Atlantic and loved it.

Mountain waves are fairly common over Greenland, not sure how far out you were.

Flying westbound, the routing would normally be planned so as to avoid the core of the jet stream (which normally means you fly north of the G.C. track, but varies day to day), but you might have been crossing it.

As for the A330, the A/THR is usually quite “lazy” and has a “soft mode” in cruise, which allows for certain speed variations, before spooling the engines. However, if the speed excursions were significant, the A/THR would intervene.

Having said that, the sounds must have been more audible in the back, rather than on the flight deck, so most likely the pilots didn’t even notice :)
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zeke
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Re: Question for Airbus A330 pilots

Wed Mar 04, 2020 3:07 pm

saab2000 wrote:

Can anyone with transatlantic experience speak to this? Do mountain wave conditions exist from the terrain in Greenland? Also, how does the Airbus autothrust work regarding fluctuations in airspeed? The 737 autothrottle is OK but not fantastic, especially at high altitudes.


Mountain waves and gravity waves are known in that area, very common. Depending on your weight and the ISA deviation the aircraft may have also been near maximum altitude for its weight. During cruise there is a “soft” altitude hold and the aircraft will sometime drop a bit of speed while maintaining that soft level. If you slow down a little it can take some time for the thrust to come back up and slowly accelerate, another wave comes, you start going towards Mmo thrust goes back to idle, and the cycles repeats.

Please see this paper for more details on the unique upper level conditions in the area. http://haraldurolafsson.com/greinar/map ... nd2009.pdf
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saab2000
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Re: Question for Airbus A330 pilots

Wed Mar 04, 2020 3:27 pm

Thanks both! I was indeed near the rear of the aircraft. It was somewhat unnerving to be honest and I’m sure they were near their maximum altitude.

Probably a non-event but I’ve never really observed this phenomenon over the Atlantic as a passenger and I’ve probably been across the Atlantic 75 times in each direction.

I prefer to cross the Rockies at a lower altitude to give the A/T system the space to do its thing with plenty of room from overspeed to underspeed. I know this is a different situation when flying across the Atlantic.
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tb727
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Re: Question for Airbus A330 pilots

Sun Mar 08, 2020 2:47 am

Any of you Airbus guys find selecting the speed and activating the approach phase at cruise level helpful to get quicker thrust changes with the A/T to get better airspeed control in wave/turbulence? After you are through the wave/turbulence you just re-cruise it so it can go back into soft cruise mode. Just wondering if anyone does it.
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Starlionblue
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Re: Question for Airbus A330 pilots

Sun Mar 08, 2020 2:56 am

tb727 wrote:
Any of you Airbus guys find selecting the speed and activating the approach phase at cruise level helpful to get quicker thrust changes with the A/T to get better airspeed control in wave/turbulence? After you are through the wave/turbulence you just re-cruise it so it can go back into soft cruise mode. Just wondering if anyone does it.


Going to selected speed is appropriate as it gets you out of soft cruise. Indeed, decreasing the speed target is the method specified in the FCTM sections on "Overspeed Prevention" and "Overspeed Recovery".

I don't see why you would activate the approach phase, as it would not make a difference to the situation. The flight phase doesn't have an effect on autothrust if you are in selected speed.
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johns624
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Re: Question for Airbus A330 pilots

Sun Mar 08, 2020 3:00 pm

Haven't seen ya online lately Saab. I remember you from the old Serotta forum.
 
Alias1024
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Re: Question for Airbus A330 pilots

Sun Mar 08, 2020 9:44 pm

tb727 wrote:
Any of you Airbus guys find selecting the speed and activating the approach phase at cruise level helpful to get quicker thrust changes with the A/T to get better airspeed control in wave/turbulence? After you are through the wave/turbulence you just re-cruise it so it can go back into soft cruise mode. Just wondering if anyone does it.


Selected speed absolutely. I’ve honestly never seen anyone activate approach phase in mountain wave.
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tb727
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Re: Question for Airbus A330 pilots

Tue Mar 10, 2020 12:38 am

Starlionblue wrote:
tb727 wrote:
Any of you Airbus guys find selecting the speed and activating the approach phase at cruise level helpful to get quicker thrust changes with the A/T to get better airspeed control in wave/turbulence? After you are through the wave/turbulence you just re-cruise it so it can go back into soft cruise mode. Just wondering if anyone does it.


Going to selected speed is appropriate as it gets you out of soft cruise. Indeed, decreasing the speed target is the method specified in the FCTM sections on "Overspeed Prevention" and "Overspeed Recovery".

I don't see why you would activate the approach phase, as it would not make a difference to the situation. The flight phase doesn't have an effect on autothrust if you are in selected speed.


Does going from ALTCRZ to ALT change anything?
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Starlionblue
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Re: Question for Airbus A330 pilots

Tue Mar 10, 2020 2:48 am

tb727 wrote:
Starlionblue wrote:
tb727 wrote:
Any of you Airbus guys find selecting the speed and activating the approach phase at cruise level helpful to get quicker thrust changes with the A/T to get better airspeed control in wave/turbulence? After you are through the wave/turbulence you just re-cruise it so it can go back into soft cruise mode. Just wondering if anyone does it.


Going to selected speed is appropriate as it gets you out of soft cruise. Indeed, decreasing the speed target is the method specified in the FCTM sections on "Overspeed Prevention" and "Overspeed Recovery".

I don't see why you would activate the approach phase, as it would not make a difference to the situation. The flight phase doesn't have an effect on autothrust if you are in selected speed.


Does going from ALTCRZ to ALT change anything?


You only get "A/THR soft mode" in ALT CRZ, so that would have an effect, but only if you're in managed speed. You get the same effect by going to selected speed.
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tb727
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Re: Question for Airbus A330 pilots

Tue Mar 10, 2020 8:42 pm

Starlionblue wrote:
tb727 wrote:
Starlionblue wrote:

Going to selected speed is appropriate as it gets you out of soft cruise. Indeed, decreasing the speed target is the method specified in the FCTM sections on "Overspeed Prevention" and "Overspeed Recovery".

I don't see why you would activate the approach phase, as it would not make a difference to the situation. The flight phase doesn't have an effect on autothrust if you are in selected speed.


Does going from ALTCRZ to ALT change anything?


You only get "A/THR soft mode" in ALT CRZ, so that would have an effect, but only if you're in managed speed. You get the same effect by going to selected speed.


Gotcha, thanks!
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saab2000
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Re: Question for Airbus A330 pilots

Tue Mar 10, 2020 10:25 pm

johns624 wrote:
Haven't seen ya online lately Saab. I remember you from the old Serotta forum.


Lurker here these days!
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