jmhLUV2fly
Posts: 539
Joined: Tue Dec 14, 1999 4:15 pm

FL 717 Takeoff Power Application Question.

Mon Jul 10, 2006 5:27 pm

This question would be for those AirTran 717 pilots out there.
I have noticed on several occasions recently that when AirTran 717's begin the takeoff role, the application of power is gradual, I have noticed this almost exact process on probably 4 or 5 717's in Pensacola.
So my question to those who would know the answer, has AirTran's flight department instructed its crews to follow a certain takeoff/application of power procedure now?
I remember many years back when Delta's MD-88 has its accident of all places here in Pensacola, with the engine failing and thereafter crews were told to gradually apply power, give those fan blades a chance to spool up.
Anyway, just thought I would ask, just curious, perhaps it was circumstance but something suggest to me otherwise.
Any info would be great.
JMH-Pensacola, Florida!
 
OV735
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Joined: Sat Jan 17, 2004 8:49 am

RE: FL 717 Takeoff Power Application Question.

Sun Jul 23, 2006 9:05 pm

As far as I know, it's a common practice on all high-bypass turbofans. Throttles are not thrown into takeoff position in one instance, but rather gradually pushed to around half-way (40% N1 on the 737-3/4/500, if I'm not mistaken), and after the engines have stabilised, TO/GA mode is engaged.

Hopefully someone can give a more detailed explanation.

Cheers,
OV735
 
SlamClick
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RE: FL 717 Takeoff Power Application Question.

Sun Jul 23, 2006 11:40 pm

If your observation is limited to one airport it might be related to that. There are runways with displaced thesholds where you may take the active at the very beginning of the runway but not apply full takeoff power until passing a certain point. Runways 01L and R at SFO are like this.

I haven't been into PNS since 1967 and unfortunately GoogleEarth doesn't have most of the airport in high-res so I can't answer my own question. But it could be that departures have some such restriction.

It is true that the power application might be somewhat gradual ("stand them up and press TOGA" kind of thing) but it should not be quite so noticeabl.
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Eddie757
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Joined: Sun Jul 23, 2006 7:07 pm

RE: FL 717 Takeoff Power Application Question.

Mon Jul 24, 2006 1:03 am

Concerning this, I can add that depending on the brand of the engines, the apply of thrust in a normal take off (not rolling) is different. According to the tests, it has been proved that with some kind of wind components (normally tailwinds), there is a sudden loss of power when applying t/o thrust in a "not progessive way". So in some engines, you have to reach some amount of... EPR or N1,N2 or whatever... initially, and then apply t/o thrust gradually. This changes from one brand or kind of engine to another.
 
undehoulli
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RE: FL 717 Takeoff Power Application Question.

Mon Jul 24, 2006 1:08 am

I've only ridden up front on the 717 once so far and it was a few months ago - if I remember correctly, autothrottles were used to set the takeoff power setting. Don't know if that might have something to do with your question.

I should also add that this wasn't on an FL 717 either...

[Edited 2006-07-23 18:12:02]
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Eddie757
Posts: 21
Joined: Sun Jul 23, 2006 7:07 pm

RE: FL 717 Takeoff Power Application Question.

Mon Jul 24, 2006 1:13 am

Quoting Undehoulli (Reply 4):
if I remember correctly, autothrottles were used to set the takeoff power setting

In normal operation the T/O power is applyed with autothrottle in most of the operations. Nevertheless, there's an initial power that you select manually, as I said, before switching the A/T on.

This practice, when is required, is done in manual as well as in autothrottle take offs. Normally when you are doing a rolling take off, it is not necessary as you are entering the runway in fact with power.
 
rendezvous
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Joined: Sun May 20, 2001 9:14 pm

RE: FL 717 Takeoff Power Application Question.

Mon Jul 24, 2006 9:29 am

Well any plane with FADEC will control how fast the throttles can go up anyway. Sure, you can smack them forward as fast as you want, and the computer will do the rest - add fuel and change vanes etc at the right speed so nothing is damaged or exceeded.

From what I've experienced taking off in jets, the throttles are spooled up a bit, then increased to the takeoff thrust.
 
vikkyvik
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Joined: Thu Jul 31, 2003 1:58 pm

RE: FL 717 Takeoff Power Application Question.

Mon Jul 24, 2006 10:05 am

Quoting SlamClick (Reply 2):
If your observation is limited to one airport it might be related to that. There are runways with displaced thesholds where you may take the active at the very beginning of the runway but not apply full takeoff power until passing a certain point. Runways 01L and R at SFO are like this.

I haven't been into PNS since 1967 and unfortunately GoogleEarth doesn't have most of the airport in high-res so I can't answer my own question. But it could be that departures have some such restriction.

According to airnav.com, neither of PNS's two runways has a displaced threshold.

Would this restriction be due to objects that could be damaged by jetblast located at the arrival end of the runway?

~Vik
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speedracer1407
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Joined: Fri Dec 24, 2004 4:19 pm

RE: FL 717 Takeoff Power Application Question.

Mon Jul 24, 2006 11:18 am

in my experience, based on both my observations aboard various flights and similar questions that I've asked on this forum, the spool-up speed is mostly dependent on the pilot. Old, slow spooling turbojets or very low bypass are, I think, a different story. But modern, FADEC controled engine, as far as I know, are all capable of spooling up VERY quick. On a recent multi-leg flight on an ERJ, for example, two takeoffs were performed with gradual application of thrust. The other two were spooled up from near idle to takeoff in maybe a a second or so. Similarly, almost every A320 flight I've been on recently has surprised me with its speedy spoolup. Even older MD-80s seem to be able to snap up to Takeoff thrust quickly, while some pilots appear to choose a very gradual spoolup.
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bri2k1
Posts: 952
Joined: Sun Dec 19, 2004 4:13 am

RE: FL 717 Takeoff Power Application Question.

Mon Jul 24, 2006 10:09 pm

Quoting Vikkyvik (Reply 7):
Would this restriction be due to objects that could be damaged by jetblast located at the arrival end of the runway?

I don't think so. Once you're on the runway surface and aligned with the runway centerline, you should be able to firewall it with no damage to stuff on the ground.
Position and hold
 
flymatt2bermud
Posts: 551
Joined: Tue Jan 31, 2006 11:58 am

RE: FL 717 Takeoff Power Application Question.

Tue Jul 25, 2006 3:24 am

Our aircraft has the same Rolls Royce engines as the 717's. It seems everybody is correct. If you slam the throttles to the firewall FADEC will make a slow acceleration to about 60% then bring them up a bit more briskly. If you use Auto Throttle it's the same affect gradual at first then here they come. If there is a takeoff crosswind component of more than 20 knots, the limitations say we must accelerate to 30 KIAS prior to 66% then bring the throttles up the rest of the way.
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