Hey fellows of this community. I have a question concerning about the correct way to startup the engines of this magnificent flying machine. More especificic I can say that I'm starting the engines using AUTOSTART option but I don´t know which percentage of N2, gives me the permission to move the fuel control lever for fuel feeding, I have read in FCOM manuals but they don´t show the step by step procedure and percentages of N2.

 

Another question, is that correct to derate the engines for short flights until rates of 80. (this is lower rates than TO-1 or TO.-2 this gives derate about 89 or 92).

 

Thanks in advance

 

:unknw:

 

 

 

More especificic I can say that I'm starting the engines using AUTOSTART option but I don´t know which percentage of N2, gives me the permission to move the fuel control lever for fuel feeding, I have read in FCOM manuals but they don´t show the step by step procedure and percentages of N2.

 

In AUTOSTART, the aircraft controls the addition of fuel to ensure it kicks in at the proper engine speed.  This isn't the NG anymore.  All you do is monitor to make sure the plane doesn't screw anything up, really.

 

The procedure (depending on the company SOP) is generally to select the engine start on the side you want, and then set the cutoff switch to RUN when you see an engine oil pressure indication.  This is not required, however, and you could just as well set the cutoff to RUN and then select the starter for the appropriate side.

Yes, as mentioned typical procedure is to engage the starter and then fuel cutoff to RUN. You should monitor engine indications for oil pressure increasing and any potential problems but the aircraft also monitors the start and will automatically abort the start if abnormalities are detected.

Also the 777 APU is powerful enough to start both engines at once, though I'm not sure if this is common practice among airlines. Seems better practice to monitor the start of the engines one at a time. 

I'd go with something like the following:

 

• APU: Running & on Electrical Bus & bleed air
• Clearance to start: Recieved
• Lights: Beacon on
• Hydraulics: on
• Fuel pumps: on
• Packs: Auto
• Lower EICAS: Monitor Engine parameters.
• Engine Start selector: on (Left or Right)
• Fuel Cutoff Selector: Run (Left or right as above).
• Monitor engine parameters

How high an N2 do you need before you select the Fuel selector to Run?
anything higher than 0% is fine!
(even 0% is fine)

Also the 777 APU is powerful enough to start both engines at once, though I'm not sure if this is common practice among airlines. Seems better practice to monitor the start of the engines one at a time. 

 

On the RR and PW engines you can do that but not with the GE's as far as I know.

 

 

Also the 777 APU is powerful enough to start both engines at once, though I'm not sure if this is common practice among airlines.

 

It depends...see below.

 

On the RR and PW engines you can do that but not with the GE's as far as I know.

 

This is my understanding as well.

 

Additionally, you have to consider the equippage on the ground as well.  Most ground service providers have powerful enough equipment for large aircraft, but the idle thrust of both of those fans is enough to make it tough to push the plane back on some equipment.  As such, some stations ("stations" = "airports") have local SOPs to only start one before/during the push, and the second after the push ends.

 

Next time you're a passenger on a round trip, try to listen for any differences between the two stations (ideally on a 777, but even smaller aircraft can cause issues: a fully loaded CR7 with both engines turning is enough to put a stand up Lektro tug on its knees).

Does cabin comfort come into play? For example all the vibration from those 2 mammoth engines spooling up out of sync with each other.

 

Eric W

Does cabin comfort come into play? For example all the vibration from those 2 mammoth engines spooling up out of sync with each other.

 

My thought would be no, though I can't say that definitively.  They're going to be out of sync during each start anyway, and the out of sync condition only really drives beats (in a tonal sense, the "wah wah wah wah wah" of the two different frequencies) until the engines stablize.  The vibration will happen simply as a part of the start sequence.

 

In theory, starting them together would minimize the beats (if they both kick in at the same exact time), and the vibration caused by the start would only happen once (again, assuming both engines start at the same time).

 

In a different example, however, cabin comfort does come into play:

On the 737, some operators will start #2, close the ISOL VALVE, set Pack #2 to AUTO, and then start #1.  This allows the #2 engine to supply bleed air to the #2 pack to keep the cabin warm/cool on extreme temp days for passenger comfort, while engine #1 starts off of the APU (with the #1 pack off).

 

Then again, others just keep the packs off until both engines are started.

 

Either way, that's mostly for temperature and not vibration/sound.  The sound issue is a lot more prevalent on props (which is why many prop planes have prop syncrophasers, as you see on the JS4100).

It depends...see below.

 

 

This is my understanding as well.

 

Additionally, you have to consider the equippage on the ground as well.  Most ground service providers have powerful enough equipment for large aircraft, but the idle thrust of both of those fans is enough to make it tough to push the plane back on some equipment.  As such, some stations ("stations" = "airports") have local SOPs to only start one before/during the push, and the second after the push ends.

 

Next time you're a passenger on a round trip, try to listen for any differences between the two stations (ideally on a 777, but even smaller aircraft can cause issues: a fully loaded CR7 with both engines turning is enough to put a stand up Lektro tug on its knees).

 

AA has 777 capable towbars and tugs at ORD but Qatar still waits until push is complete before starting engines while AA sometimes starts one engine during push. I've seen AA start both at the same time during push only a couple of times (RR engines)