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SFO Departures And Engine Throttle Backs  
User currently offlinederwentwater747 From United States of America, joined Apr 2012, 9 posts, RR: 0
Posted (1 year 6 months 3 weeks 3 days 23 hours ago) and read 2403 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

13 replies: All unread, jump to last
 
User currently offlineTupolevTu154 From Germany, joined Aug 2004, 2178 posts, RR: 28
Reply 1, posted (1 year 6 months 3 weeks 3 days 22 hours ago) and read 2382 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.



Atheists - Winning since 33 A.D.
User currently offlineStarlionblue From Greenland, joined Feb 2004, 16991 posts, RR: 67
Reply 2, posted (1 year 6 months 3 weeks 3 days 17 hours ago) and read 2265 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.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineIAHFLYR From United States of America, joined Jun 2005, 4790 posts, RR: 22
Reply 3, posted (1 year 6 months 3 weeks 3 days 17 hours ago) and read 2260 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.



Any views shared are strictly my own and do not a represent those of any former employer.
User currently offlineStarlionblue From Greenland, joined Feb 2004, 16991 posts, RR: 67
Reply 4, posted (1 year 6 months 3 weeks 3 days 17 hours ago) and read 2259 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.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineIAHFLYR From United States of America, joined Jun 2005, 4790 posts, RR: 22
Reply 5, posted (1 year 6 months 3 weeks 3 days 16 hours ago) and read 2250 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.



Any views shared are strictly my own and do not a represent those of any former employer.
User currently offlinesoon7x7 From , joined Dec 1969, posts, RR:
Reply 6, posted (1 year 6 months 3 weeks 3 days 16 hours ago) and read 2245 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


User currently offlineJBirdAV8r From United States of America, joined Jun 2001, 4488 posts, RR: 21
Reply 7, posted (1 year 6 months 3 weeks 3 days 12 hours ago) and read 2169 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.



I got my head checked--by a jumbo jet
User currently offlineStarlionblue From Greenland, joined Feb 2004, 16991 posts, RR: 67
Reply 8, posted (1 year 6 months 3 weeks 3 days 11 hours ago) and read 2164 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. 



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineJBirdAV8r From United States of America, joined Jun 2001, 4488 posts, RR: 21
Reply 9, posted (1 year 6 months 3 weeks 3 days 11 hours ago) and read 2160 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 



I got my head checked--by a jumbo jet
User currently offlineStarlionblue From Greenland, joined Feb 2004, 16991 posts, RR: 67
Reply 10, posted (1 year 6 months 3 weeks 3 days 8 hours ago) and read 2114 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. 



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlinevikkyvik From United States of America, joined Jul 2003, 9763 posts, RR: 27
Reply 11, posted (1 year 6 months 3 weeks 3 days 2 hours ago) and read 2032 times:
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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!



"Two and a Half Men" was filmed in front of a live ostrich.
User currently offlinefuturesdpdcop From United States of America, joined Feb 2006, 1293 posts, RR: 5
Reply 12, posted (1 year 6 months 3 weeks 2 days 22 hours ago) and read 1997 times:

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

User currently onlinetimz From United States of America, joined Sep 1999, 6771 posts, RR: 7
Reply 13, posted (1 year 6 months 3 weeks 2 days 21 hours ago) and read 1975 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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