alphonze
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SIN: Noise Abatement Or Weird Takeoff?

Fri Nov 15, 2013 7:22 am

I wonder if any of the gurus here can shed any light. I was on a CX A330 SIN-HKG last night. We took off about 9pm. Normal take off, until just after the *clunk* of the gear doors closing, some 30 seconds after leaving the ground. Then very suddenly the engines spooled up hard and I could feel the seat pushing into my back. Some seconds after that, the engines spooled right down again to almost silence - which is damnably eerie only one minute into a climbout - and then they wound up again and everything proceeded normally.

I fly about 30-40 times a year, and have never experienced a take off quite like that one. Is there a noise abatement at SIN which requires low thrust until you're out over the water? Or what the hell else could it have been?
 
7seven7
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RE: SIN: Noise Abatement Or Weird Takeoff?

Fri Nov 15, 2013 7:45 am

It could just be that it was a light load and the take off thrust setting (FLEX on Airbus) was such that it was below the climb thrust setting they'd chosen to use. Assuming acceleration height is 1000' AAL, this is the point they'd move the thrust levers from FLEX to climb and you may hear and feel the associated increase in oomf (technical tern).

Quite common on a 77W doing a very short sector with a light load. Also helps to reduce numbers such as Vmcg to allow for a lower V1 speed.
 
speedbird128
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RE: SIN: Noise Abatement Or Weird Takeoff?

Fri Nov 15, 2013 8:22 am

Hiya!

Quoting 7seven7 (Reply 1):
the take off thrust setting (FLEX on Airbus) was such that it was below the climb thrust setting

Granted I am not a commercial pilot - however in my interaction with pilots and sim time and fam flights - I have been led to believe that FLEX/reduced take off thrust settings would never be below climb thrust setting....?

Have I been misinformed?
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CCA
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RE: SIN: Noise Abatement Or Weird Takeoff?

Fri Nov 15, 2013 8:53 am

Yes, on occasion reduced thrust takeoffs are below CLB thrust.

On the 744 RR a D-TO2 56C for example is below CLB2 so the thrust increases when climb thrust is set.

It's well below CLB1 and obviously CLB.

Singapore has a height limitation on departure during certain times of the day, often the runway length leads to a low thrust takeoff however the crew ARM a high climb thrust to meet the altitude restriction. So the thrust increases substantially when climb thrust is selected, once the restriction has been met the crew select a low climb thrust through the FMC.
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PGNCS
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RE: SIN: Noise Abatement Or Weird Takeoff?

Fri Nov 15, 2013 3:46 pm

Quoting Speedbird128 (Reply 2):
Granted I am not a commercial pilot - however in my interaction with pilots and sim time and fam flights - I have been led to believe that FLEX/reduced take off thrust settings would never be below climb thrust setting....?

Have I been misinformed?

In addition to what CCA said, the ability to derate or flex TO thrust below climb thrust is aircraft type dependent. Some aircraft will allow it and some will not.
 
speedbird128
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RE: SIN: Noise Abatement Or Weird Takeoff?

Fri Nov 15, 2013 3:56 pm

Quoting PGNCS (Reply 4):
Some aircraft will allow it and some will not.

Very good thanks all for the feedback. It might have been an airframe limitation then... I don't remember if it was Airbus or Boeing I have lost track...  
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tb727
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RE: SIN: Noise Abatement Or Weird Takeoff?

Fri Nov 15, 2013 4:10 pm

Quoting PGNCS (Reply 4):
In addition to what CCA said, the ability to derate or flex TO thrust below climb thrust is aircraft type dependent. Some aircraft will allow it and some will not.

I've heard it both ways and almost started a thread about it. I won't have the FE give me reduced takeoff numbers below initial climb EPR even though we can. We are still checking off the reduced box on the logpage and the throttles are set for the climb already. We don't track/record specific data on takeoff thrust used other than just checking a Max or Reduced box for each leg.
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PGNCS
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RE: SIN: Noise Abatement Or Weird Takeoff?

Fri Nov 15, 2013 4:36 pm

Quoting tb727 (Reply 6):
Quoting PGNCS (Reply 4):In addition to what CCA said, the ability to derate or flex TO thrust below climb thrust is aircraft type dependent. Some aircraft will allow it and some will not.
I've heard it both ways and almost started a thread about it. I won't have the FE give me reduced takeoff numbers below initial climb EPR even though we can. We are still checking off the reduced box on the logpage and the throttles are set for the climb already. We don't track/record specific data on takeoff thrust used other than just checking a Max or Reduced box for each leg.

We were not allowed to on any JT-8D aircraft I have flown, but that doesn't mean it's a restriction on the engine, it may have been procedural on our end in some cases I really don't know and your experience bears that out. On other more automated aircraft you will sometimes get higher climb thrust automatically when it's selected but like I said it's type dependent. For instance, MD-80's (at least the ones I have seen) won't give a flex TO setting lower than climb thrust, but MD-90's will. There are other examples but I use that to show how aircraft/engine specific it is.
 
XFSUgimpLB41X
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RE: SIN: Noise Abatement Or Weird Takeoff?

Fri Nov 15, 2013 7:20 pm

On Airbus aircraft, due to the throttle quadrant logic, climb power will not be below takeoff power (since you have to move the thrust levers back from the flex/mct detent to the CLB detent).

On boeings, it is common for climb power to be above takeoff power... I've seen a 9% increase.
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speedbird128
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RE: SIN: Noise Abatement Or Weird Takeoff?

Fri Nov 15, 2013 11:20 pm

Quoting tb727 (Reply 6):
Quoting PGNCS (Reply 7):
Quoting XFSUgimpLB41X (Reply 8):

Many thanks guys! I have learned something new today! Appreciate the comprehensive answers!
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XFSUgimpLB41X
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RE: SIN: Noise Abatement Or Weird Takeoff?

Sat Nov 16, 2013 4:24 am

Got it back asswards   I meant to say:

Quoting XFSUgimpLB41X (Reply 8):

On Airbus aircraft, due to the throttle quadrant logic, takeoff power will not be below climb power (since you have to move the thrust levers back from the flex/mct detent to the CLB detent).

I think you got what I meant to say though!
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musang
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RE: SIN: Noise Abatement Or Weird Takeoff?

Sat Nov 16, 2013 9:13 pm

I don't think anyone's commented on this yet:

Quoting alphonze (Thread starter):
Some seconds after that, the engines spooled right down again to almost silence

I'm familiar with the concept of thrust increase from t/o to Climb (737 classics) and having been understandably taken aback by that, a significant reduction might well have taken you by surprise! The only reason I can think of for the reduction is an altitude restriction shortly after take-off.

Many SIDs (Standard Instrument Departures) have altitude restrictions, at which we level out, anywhere from 3000 feet to a flight level, and I'm not SIN experienced. Often ATC comes in with an instruction which over-rides the SID, perhaps negating the altitude restriction and allowing further climb without levelling out.

Alternately, which could explain your flight, ATC instructed a low level out due to conflicting traffic. If there was also a speed restriction there would be a thrust reduction when levelling out.

Regards - musang
 
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zeke
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RE: SIN: Noise Abatement Or Weird Takeoff?

Mon Nov 18, 2013 5:10 am

Quoting alphonze (Thread starter):

Singapore has some close in constraints, you took off to the NE, there is a close in altitude and speed constraint of 2000ft and 220 kts, it is common at times to get given a vector or direct to a waypoint when contacting departures at quieter times. The aircraft you were in also was around 50t below MTOW, so it had a lot of performance.

What you would have herd is a close in level off at a low speed like 220ks, and then a higher speed climb.

Quoting XFSUgimpLB41X (Reply 8):

Depends if it is a flex or derate, if it is a derate, climb can be above takeoff, as the derate is reducing the rated thrust.
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ZSOFN
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RE: SIN: Noise Abatement Or Weird Takeoff?

Mon Nov 18, 2013 8:53 am

I recently flew with SQ MAN-MUC and back (77W); obviously very short sectors and in both directions low load factors; I noticed in both cases the takeoff seemed quite leisurely, with power actually then increasing after ~2000ft. I assumed the same; not technically "FLEX" but a significant derate for takeoff with power then being increased for CLB.
 
XFSUgimpLB41X
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RE: SIN: Noise Abatement Or Weird Takeoff?

Tue Nov 19, 2013 1:32 am

Quoting zeke (Reply 12):
Depends if it is a flex or derate, if it is a derate, climb can be above takeoff, as the derate is reducing the rated thrust.

Not sure about the A300/10, but on the 20/30/40/80 derated takeoff thrust cannot be below climb thrust due to throttle logic.
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zeke
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RE: SIN: Noise Abatement Or Weird Takeoff?

Tue Nov 19, 2013 3:14 am

We are addicted to our thoughts. We cannot change anything if we cannot change our thinking – Santosh Kalwar
 
AJ
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RE: SIN: Noise Abatement Or Weird Takeoff?

Wed Nov 20, 2013 6:10 am

At that time of night the ATIS has advice to maintain 3,000ft unless otherwise advised by ATC.
 
XFSUgimpLB41X
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RE: SIN: Noise Abatement Or Weird Takeoff?

Wed Nov 20, 2013 8:19 am

Quoting zeke (Reply 15):
Have a look at pages 17&18 of this http://www.smartcockpit.com/download...b.pdf

Nice find!

I always associated the RPM increase with the cleanup and acceleration to 250, not an adjustment to the higher than flex TO climb RPM. It is a far less dramatic process than going to climb power on the boeing.

Those details are not included in our manuals. Thanks!
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