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Topic: SFO Departures And Engine Throttle Backs
Username: derwentwater747
Posted 2012-12-29 11:15:02 and read 2623 times.

Whenever I take off from SFO the engine seems like it's cut to idle at roughly 3,000ft. Is this a departure requirement ...not sure why since we are over water? Or do I have bad luck,and it's TCAS alerts?

Thx

Topic: RE: SFO Departures And Engine Throttle Backs
Username: TupolevTu154
Posted 2012-12-29 12:15:58 and read 2602 times.

Quoting derwentwater747 (Thread starter):
Whenever I take off from SFO the engine seems like it's cut to idle at roughly 3,000ft. Is this a departure requirement ...not sure why since we are over water? Or do I have bad luck,and it's TCAS alerts?

I would hazard an educated guess that this is the engines going from take-off power (or 'Flex' as it's known in the Airbus) back to climb power. Sometimes it is very noticeable especially when the engines are at or near TOGA (Take off/Go Around, or max thrust in the Airbus).

Obviously SOP's differ from aircraft to aircraft and airline to airline, but some passengers can be startled by the change in engine noise when going from flex to cruise.

Topic: RE: SFO Departures And Engine Throttle Backs
Username: Starlionblue
Posted 2012-12-29 17:47:22 and read 2485 times.

Quoting derwentwater747 (Thread starter):
Whenever I take off from SFO the engine seems like it's cut to idle at roughly 3,000ft. I

Not idle. Definitely not idle at 3000 feet. As TupolevTu154 says, the decrease is from take-off power to climb power. This is to decrease wear and tear on the engines. The airplane will normally still be accelerating and climbing after the decrease so you're still at a high power setting. AFAIK the only planes where climb power is the same as take-off power are small GA planes with fixed-pitch props.

I've experienced once or twice that the pilots weren't as gentle as they could be throttling back and the wings have shaken violently, with the whole plane shuddering.

Topic: RE: SFO Departures And Engine Throttle Backs
Username: IAHFLYR
Posted 2012-12-29 17:55:15 and read 2480 times.

My thought is it's not at 3,000 feet but more like 1,000 feet where the throttles are brought from takeoff power to climb power, at times I've found it to be an increase in thrust settings rather than the normal reduction in thrust settings.....normally associated with the first change in flap settings to clean up the airplane.......all just IMHO of course.

I'm flying out of SFO on an A320 in a couple of days, so I'll be sure to pay special attention to anything like what the OP has referenced.

Topic: RE: SFO Departures And Engine Throttle Backs
Username: Starlionblue
Posted 2012-12-29 17:57:07 and read 2479 times.

Quoting IAHFLYR (Reply 3):
at times I've found it to be an increase in thrust settings rather than the normal reduction in thrust settings.....normally associated with the first change in flap settings to clean up the airplane.......all just IMHO of course.

I think this is a perceived increase due to the decreased drag. The engines can stay at the same setting but with the flaps coming up the acceleration increases.

Topic: RE: SFO Departures And Engine Throttle Backs
Username: IAHFLYR
Posted 2012-12-29 18:15:17 and read 2470 times.

Quoting Starlionblue (Reply 4):
I think this is a perceived increase due to the decreased drag. The engines can stay at the same setting but with the flaps coming up the acceleration increases.


Oh for sure however; some guys I know who fly B73NG's have told me in certainly weather conditions with long runways the reduced power settings for takeoff do create an increase in thrust settings around 1,000 feet. I certainly have no first hand knowledge other than in a few full motion sims, so my very limited knowledge is from what they tell me or have seen on a jump seat.

Topic: RE: SFO Departures And Engine Throttle Backs
Username: soon7x7
Posted 2012-12-29 18:25:13 and read 2465 times.

Quoting derwentwater747 (Thread starter):
Whenever I take off from SFO the engine seems like it's cut to idle at roughly 3,000ft. Is this a departure requirement ...not sure why since we are over water? Or do I have bad luck,and it's TCAS alerts?


Think I may know this...when we depart ISP at about 1200ft for noise abatement, throttle back just a bit , clean the wings , climb to 4,000 and throttle back a lot till we leave class Charlie airspace. It also is a track that conflicts with descending inbounds from over the Atlantic to JFK. Once we depart class C and execute a turn to the south it is great guns! In short, might have to do something with airspace conflicts with other regularly scheduled traffic in the area. Just guessing here...j

Topic: RE: SFO Departures And Engine Throttle Backs
Username: JBirdAV8r
Posted 2012-12-29 22:24:03 and read 2389 times.

Quoting Starlionblue (Reply 2):
AFAIK the only planes where climb power is the same as take-off power are small GA planes with fixed-pitch props.

In the jets that I fly, climb N1 settings can match (and often times exceed) the flex takeoff N1s. Max thrust takeoffs generally result in an N1 reduction at climb power.

Topic: RE: SFO Departures And Engine Throttle Backs
Username: Starlionblue
Posted 2012-12-29 23:23:42 and read 2384 times.

Quoting JBirdAV8r (Reply 7):
Quoting Starlionblue (Reply 2):
AFAIK the only planes where climb power is the same as take-off power are small GA planes with fixed-pitch props.

In the jets that I fly, climb N1 settings can match (and often times exceed) the flex takeoff N1s. Max thrust takeoffs generally result in an N1 reduction at climb power.

Fair enough. But as you say that's flex take-off power, not full take-off power. In a Cessna 172 you just push the knob all the way in for take-off and any climb. 

Topic: RE: SFO Departures And Engine Throttle Backs
Username: JBirdAV8r
Posted 2012-12-29 23:41:30 and read 2380 times.

Quoting Starlionblue (Reply 8):
. But as you say that's flex take-off power, not full take-off power.

Well, yes, but flex takeoffs are the norm, rather than the exception, for most jet transport aircraft.

And Flex in a 172 is not recommended 

Topic: RE: SFO Departures And Engine Throttle Backs
Username: Starlionblue
Posted 2012-12-30 02:34:16 and read 2334 times.

Quoting JBirdAV8r (Reply 9):
And Flex in a 172 is not recommended 

I never really wanted to try. In many cases (heavy instructor, high temperature) I was desperately trying to shove the throttle control just a bit further in. 

Topic: RE: SFO Departures And Engine Throttle Backs
Username: vikkyvik
Posted 2012-12-30 08:58:18 and read 2252 times.

Quoting derwentwater747 (Thread starter):
Whenever I take off from SFO the engine seems like it's cut to idle at roughly 3,000ft.

I find it a very interesting phenomenon when flap setting is reduced and/or thrust is reduced to climb thrust. Your body gets used to the acceleration it's feeling during initial climb. Then when that vertical and/or horizontal acceleration is reduced, it can feel like you just lost all engines and are suddenly plummeting, when in fact you're still accelerating forward and climbing.

I suppose that's why they tell pilots to trust their instruments.  
Quoting Starlionblue (Reply 10):
In many cases (heavy instructor, high temperature)

That cracked me up!

Topic: RE: SFO Departures And Engine Throttle Backs
Username: futuresdpdcop
Posted 2012-12-30 12:30:27 and read 2217 times.

Are you departing off the 1's? It could be to stay below traffic departing 29 at OAK.

Topic: RE: SFO Departures And Engine Throttle Backs
Username: timz
Posted 2012-12-30 13:37:41 and read 2195 times.

No, SFO runway 1 departures are supposed to be at 3000 ft or above by the time they reach the OAK area; it's the OAK departure that says not to exceed 2000 ft until 4 DME.

(Likewise, rainy-weather approaches to SFO runways 19 stay above the aircraft approaching OAK rwy 11.)


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