Engine Start-Up Sequence/Process

JAGflyer · Sat Sep 19, 2015 12:28 am

On aircraft which have pneumatic engine starters (which use high pressure bleed air from another engine, the APU, or an external cart) I've noticed a standard sequence of events. I'd like to verify whether I am understanding the process right.

1. When I get on the aircraft, the air system is running off the APU. Air is coming down from the gasper vents in the cabin to provide heating/cooling.
2. During or shortly after pushback, the cabin goes quiet as the cabin air stops. At this point, I imagine this is due to all the pneumatics being directed to the starter to begin starting the first engine.
3. I hear the engine begin to spool up and start. Engine is now at idle.
4. The lights may flicker once as the supply of power is shifted from the APU to the IDG on the started engine. I can also hear the "pop" sound I'm used to hearing when an AME turns the ground service power on a dark aircraft.
5. The air system starts again in the cabin as the APU and/or the started engine can handle it with enough pneumatics to supply the next engine's starter.
6. The other engine(s) are started off the APU bleed or engine bleed.

Do I have this about right? I imagine the pilots are manually switching the bleed air switches and electric supply during the start-up sequence on the Boeing aircraft (Airbus is more automated I think). I've experienced a similar type of process on both 737s and 767s.

[Edited 2015-09-18 17:37:12]

gcb5196 · Sat Sep 19, 2015 1:11 am

Sounds about right.

1. Or the plane is connected to ground air.
2. Pretty much, this is when most people check to see if their gasper is open.
3. Yup. Also see 5/6
4. Embraer has a different way for power transfer to avoid the hard transfer, I'll have to pay better attention to see if the lights flicker next time.
5/6. Not sure for all aircraft, but for what I'm familiar with the APU has more bleed pressure than the engines do at idle. Air is provided and the other engine is started off the APU. When you do a cross bleed start the operating engine is brought out of idle to increase the bleed air pressure to start the other engine. Also you may notice that the air does not work very well when the APU is inop, even with both engines started. Pilots may taxi with the engines out of idle to increase the bleed pressure for air, but also risk overheating the brakes.

The CRJ 200 the bleeds are manual as well as power transfer. On the CRJ 7/9 and E175 they are both automatic when selected.
Hope this helps with my limited understanding of these aircraft and their systems.

JAGflyer · Sat Sep 19, 2015 1:37 am

Flying on an AC 767 yesterday, the IFE shut off when the power transferred over (right during the safety video). I'm not sure why as the transfer didn't seem any harder than previous experiences I've had. The FAs had to start a manual demo as the system takes a while too boot up.

Whiteguy · Sat Sep 19, 2015 2:34 am

Quoting Jagflyer (Thread starter):
5. The air system starts again in the cabin as the APU and/or the started engine can handle it with enough pneumatics to supply the next engine's starter.
6. The other engine(s) are started off the APU bleed or engine bleed.

Do I have this about right? I imagine the pilots are manually switching the bleed air switches and electric supply during the start-up sequence on the Boeing aircraft (Airbus is more automated I think). I've experienced a similar type of process on both 737s and 767s.

[Edited 2015-09-18 17:37:12]

On the 737 both engines are started off the APU bleed air. On the the push the bleeds are on and the packs are turned off for the start. After both engines are started, as part of the after start flow, both packs are turned on and the APU bleed air is turned off.

For an air start, number 2 is started at the gate. Once pushed you will hear the power on the #2 increase, around 40%+ for the start....

We never touch the bleed switches for the start, they are always on. Only time the get turned off is for a bleeds off take off.

mmo · Sat Sep 19, 2015 6:11 am

Quoting Jagflyer (Thread starter):
I imagine the pilots are manually switching the bleed air switches and electric supply during the start-up sequence on the Boeing aircraft (Airbus is more automated I think). I've experienced a similar type of process on both 737s and 767s.

On all the Boeing wide bodies being built today, they are as automated as Airbus is.

Quoting Jagflyer (Thread starter):
6. The other engine(s) are started off the APU bleed or engine bleed.

Generally, if you start using the APU, other engines are also started using the APU. An engine at ground idle can not provide enough bleed air to allow a successful engine start.

Woodreau · Sat Sep 19, 2015 11:55 am

One instructor had a nice jingle that goes over the things we should see during a normal engine start...
rotation, lubrication, ignition, detonation, acceleration, stabilization....

Once air is applied to the air starter, things we should see...
rotation / N2 fan
lubrication / oil pressure
ignition / ignitors on, fuel flow
detonation / ITT/EGT rise and rate of rise
acceleration / N2 N1 fan
stabilization / at engine idle after start we should see a general 2-4-6-8 N1 around 25%, 450 EGT, N2 around 65%, fuel flow 800lb/hr

About the only airplanes I see that pilots are manually switching bleeds and electrical generators are CRJ-200s, Emb-145s, and MD-80s. On most other airplanes, engine bleeds and electrical power source switchover is automatic.

fr8mech · Sat Sep 19, 2015 8:58 pm

Quoting Jagflyer (Thread starter):
On aircraft which have pneumatic engine starters (which use high pressure bleed air from another engine,

Not to be too picky, but I will be, this is not high pressure air. It is low pressure (35-45 psi, give or take a pound or 2), delivered at a high volume.

Quoting gcb5196 (Reply 1):
Embraer has a different way for power transfer to avoid the hard transfer, I'll have to pay better attention to see if the lights flicker next time.

That's called a 'no-break, power transfer,; at least it is on the MD11. Basically, the oncoming source is paralleled to the source on the buss and then the BTR (BTB) is closed. This allows a clean transfer of power. Contrast the B757/B767 where the various sources are never paralleled; there is always a flicker of lights as a source comes online or offline.

Max Q · Sat Sep 19, 2015 9:56 pm

The engine driven generators come on line automatically on the MD80, unlike the 737NG where, unbelievably
you still have to place the generators on line manually in the year 2015 !

flyDTW1992 · Sun Sep 20, 2015 12:45 am

Quoting mmo (Reply 4):
Generally, if you start using the APU, other engines are also started using the APU. An engine at ground idle can not provide enough bleed air to allow a successful engine start.

Also, there are cases when one engine will be started, APU shut down, and then a crossbleed is done to start the second engine. This happened routinely with aircraft after finishing deicing when I was working in the deicing tower.

Generally we ask for the APU to be shut down for deicing since it's usually much easier to accidentally flood an APU than it is an engine.

e38 · Sun Sep 20, 2015 1:39 am

Jagflyer, the sequence you described for engine start is correct.

There can be slight variations, of course. For example, with reference to your Step #1: "When I get on the aircraft, the air system is running off the APU." At the company where I work, in order to save fuel by not running the APU, when you get on the aircraft, the air system would be running off external air. If external air is not available, then the APU would be used; however, most stations we serve have external air available. Often you will see these units connected just on the underside of the jetway; occasionally they are positioned on top of the jetways. As an alternative, you may also see portable air carts positioned alongside the aircraft to supply conditioned air. The APU is generally started within 5 - 7 minutes of departure time and APU bleed air is used at that time. This allows the ground crew time to disconnect external power and air prior to pushback.

In your next to last sentence, you stated, "Airbus is more automated I think."

That is correct.

e38

RetiredWeasel · Sun Sep 20, 2015 2:15 am

And on the 747-400 the APU puts out enough volume that the normal procedure was to start two engines at a time. I can't remember the exact delayed engine start that was later emphasized for fuel conservation, but I think after simultaneous starts of 3 and 4, 1 was started for initial taxi and 2 was started a little later with the APU still running. mmo can probably remember more exact than me.

737tanker · Mon Sep 21, 2015 2:04 am

Quoting Whiteguy (Reply 3):

At WN when using the APU for an engine start we start the #2 first and after it is started we isolate the right side air conditioning then turn the #2 Pack so as to get air to the passengers, after that we start the #1 engine. If we are using external air for starting we reverse the procedure and start the #1 engine first.

DashTrash · Mon Sep 21, 2015 2:39 pm

On the light flickering, you are getting to watch the electrical system do its thing. In a the Dash with the APU on / engines off the main DC buses are tied. When #2 is started the buses remain tied and the entire airplane will flash. When #1 is started, then left side of the airplane will flash as the bus unties and the #1 engine driven gen picks up the load.

Now... If I remember this right, you'll get another flash of the lights when the props come out of feather and the AC generators are turned on. When they're feathered again before shutdown you'll see the system work in reverse.

I'm not typed on the DC-9 or know anything about its electrickery, but I've seen it work similarly during engine start.

Whiteguy · Tue Sep 22, 2015 4:47 am

Quoting 737tanker (Reply 11):

Quoting Whiteguy (Reply 3):

At WN when using the APU for an engine start we start the #2 first and after it is started we isolate the right side air conditioning then turn the #2 Pack so as to get air to the passengers, after that we start the #1 engine. If we are using external air for starting we reverse the procedure and start the #1 engine first.

Gotcha, every company is slightly different. Thanks

rjsampson · Tue Sep 22, 2015 5:41 pm

I'm guessing it's also possible to start the engines without turning of the PACS (which on hot days, I sometimes wish the pilots would -- I get warm very easily), presumably resulting in a longer spin-up time. Is this the case? Is it ever done?

Western727 · Tue Sep 22, 2015 6:34 pm

Quoting 737tanker (Reply 11):
At WN when using the APU for an engine start we start the #2 first

As a frequent WN flier I've noticed this. Is my assumption correct that this is an effort to "equalize" the engine run times as much as reasonably possible between engines #1 & #2, given that WN jets seemingly universally park at gates with only #1 running?

Tristarsteve · Tue Sep 22, 2015 6:57 pm

Quoting rjsampson (Reply 14):

I'm guessing it's also possible to start the engines without turning of the PACS (which on hot days, I sometimes wish the pilots would -- I get warm very easily), presumably resulting in a longer spin-up time. Is this the case? Is it ever done?

The hotter the day, the more air the starter needs to start the engine.
On an Airbus it can't be done. Selecting the start selector to start turns off the packs.
On an older Boeing you could try, but pilots do things by checklists and it is very unlikely.
In the good old days we used to leave one pack running on the Tristar while we started the first engine. Everything was manually controlled at the F/E panel, and you could see the speed that the engine was winding up. If it was hot outside and the start was slow, you could turn the pack off until the engine started. We started Nbr 3 first, and as soon as it was at idle, switched on pack nbr 3 and closed the R Xbleed, then used the APU to start the next engine.

fr8mech · Tue Sep 22, 2015 8:50 pm

Quoting Western727 (Reply 15):
As a frequent WN flier I've noticed this. Is my assumption correct that this is an effort to "equalize" the engine run times as much as reasonably possible between engines #1 & #2, given that WN jets seemingly universally park at gates with only #1 running?

I'd be very surprised if that's the case. Engines are tracked by cycles and by hours, but the hours are tied to the airframe. Only flight time is counted in the hours.

But, I will insert the standard disclaimer when dealing with aviation: there may be a case where an operator tracks actual engine hours and cycles (take-off power application). But, in almost 30 years in the business, I've never come across one.

The start order and procedure is a matter of the checklist, that's why it's the same every time.

Quoting rjsampson (Reply 14):
presumably resulting in a longer spin-up time. Is this the case?

It may also cause hot or hung starts.

AAR90 · Wed Sep 23, 2015 6:59 pm

Quoting Western727 (Reply 15):
As a frequent WN flier I've noticed this. Is my assumption correct that this is an effort to "equalize" the engine run times as much as reasonably possible between engines #1 & #2, given that WN jets seemingly universally park at gates with only #1 running?

This is Boeing's procedure. Starting #2 allows isolation of the right pneumatic system providing uninterrupted cabin air conditioning (from right PACK) before and during #1 engine start. The downside of this procedure is the procedural requirement to shutdown the #2 engine IF there are any "late bags" to be loaded after engine start --relatively rare.

Parking with #1 running is also a Boeing procedure. The preference here is that the ground crew will want to start moving cargo/bags ASAP after parking and they can't do that until the #2 engine has shutdown --saves a minute or so.

At AA we used to alternate the starting of engines based upon flight number (odd = right, even = left), but that went away many years ago. Now our manuals are virtual duplications of the Boeing manuals and... our procedures are virtual duplications of Boeing procedures.

Whiteguy · Thu Sep 24, 2015 4:29 am

Quoting AAR90 (Reply 18):

This is Boeing's procedure. Starting #2 allows isolation of the right pneumatic system providing uninterrupted cabin air conditioning (from right PACK) before and during #1 engine start. The downside of this procedure is the procedural requirement to shutdown the #2 engine IF there are any "late bags" to be loaded after engine start --relatively rare.

Parking with #1 running is also a Boeing procedure. The preference here is that the ground crew will want to start moving cargo/bags ASAP after parking and they can't do that until the #2 engine has shutdown --saves a minute or so.

At AA we used to alternate the starting of engines based upon flight number (odd = right, even = left), but that went away many years ago. Now our manuals are virtual duplications of the Boeing manuals and... our procedures are virtual duplications of Boeing procedures.

Unless it's an air start at the gate we are always on the push when engines are started anyway....your "late bags" scenario never happens....

As for parking with one running....while we often shutdown #2 while approaching the gate, it has nothing to do with ground crews opening the pits and moving bags. It's fuel saving measure, that's all. Crews don't approach the aircraft with engines on or anti collision light on at any companies I've worked at. Saving a minute or two should not take priority over safety, just my opinion....

AAR90 · Thu Sep 24, 2015 7:42 am

Quoting Whiteguy (Reply 19):
Unless it's an air start at the gate we are always on the push when engines are started anyway....your "late bags" scenario never happens....

I guess that would depend upon the airline. At AA we do the same; however, I would estimate I shutdown the #2 engine in order to accept "late bags" (during/after pushback) about 2 dozen times a year.

Quoting Whiteguy (Reply 19):
As for parking with one running....while we often shutdown #2 while approaching the gate, it has nothing to do with ground crews opening the pits and moving bags. It's fuel saving measure, that's all. Crews don't approach the aircraft with engines on or anti collision light on at any companies I've worked at. Saving a minute or two should not take priority over safety, just my opinion....

Again, depends upon the airline. AA procedure ("recommended") is to shutdown #2 engine when time/conditions permit after landing and to single-engine taxi to the gate. Upon gate arrival the ground crew is to connect ground electrical power before the engine(s) are secured unless the APU is in use --AA preference is to NOT use APU.

flyDTW1992 · Thu Sep 24, 2015 7:59 am

Quoting AAR90 (Reply 20):
Crews don't approach the aircraft with engines on or anti collision light on at any companies I've worked at

'Cept the deicers. We're crazy like that. (half joking)

Tristarsteve · Thu Sep 24, 2015 8:18 am

Quoting AAR90 (Reply 20):
Upon gate arrival the ground crew is to connect ground electrical power before the engine(s) are secured unless the APU is in use --AA preference is to NOT use APU.

And all airlines are different.
BA procedure is to always start the APU after landing, and shut down one engine for single engine taxy.
The rule for the ramp staff is.. Do not approach the aircraft until all engines are shut down and the anti collision light is off. If the APU is inop, the crew must inform ops on the radio.

We also have airlines that do not start the APU. The ramp staff need to know which airline they are meeting and what rules to follow.

gcb5196 · Thu Sep 24, 2015 3:00 pm

Quoting Whiteguy (Reply 19):
Unless it's an air start at the gate we are always on the push when engines are started anyway....your "late bags" scenario never happens....

Never say never. I have watched bag runners pull up to a plane after pushback and load bags onto a plane many times, sometimes with an engine running. It was up to the crew whether or not they were loaded.

Whiteguy · Thu Sep 24, 2015 5:09 pm

Quoting gcb5196 (Reply 23):

Quoting Whiteguy (Reply 19):
Unless it's an air start at the gate we are always on the push when engines are started anyway....your "late bags" scenario never happens....

Never say never. I have watched bag runners pull up to a plane after pushback and load bags onto a plane many times, sometimes with an engine running. It was up to the crew whether or not they were loaded.

Yeah, should've read "almost never happens".....

Depending on which airport, if you decide to load bags in the middle of the apron after push, you'll get an earfull on the apron/ground frequency....

AAR90 · Thu Sep 24, 2015 6:56 pm

Quoting flyDTW1992 (Reply 21):
Quoting AAR90 (Reply 20):
Crews don't approach the aircraft with engines on or anti collision light on at any companies I've worked at

'Cept the deicers. We're crazy like that. (half joking)

1. You're quoting the wrong person... I didn't write that.
2. You're correct... deicers are "totally crazy like that."

twal1011727 · Thu Sep 24, 2015 8:52 pm

Quoting tristarsteve (Reply 22):
We also have airlines that do not start the APU. The ramp staff need to know which airline they are meeting and what rules to follow.

Delta used to leave the APU off and arrive at the gate w/one engine only
somewhere in the last 10 yrs they changed that.

KD

Tristarsteve · Thu Sep 24, 2015 9:15 pm

Quoting TWAL1011727 (Reply 26):
Delta used to leave the APU off and arrive at the gate w/one engine only
somewhere in the last 10 yrs they changed that.

This was a totally safe practice with the MD80, but very risky with an A319.

gcb5196 · Thu Sep 24, 2015 9:29 pm

For what I'm familiar with, first flight of the day both engines are started. The #1 engine followed by #2. Single engine taxi is done on the #2 engine. The purpose as I understood it was the the #2 engine, CRJ here, provides hydraulics for the brakes in case of electric pump failure. Not sure if that is a company thing or by the manual.

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