Engine Start - No fuel pumps?

[kevinh 409]

I know the OP was, but I wasn't sure about 777cap, particularly because he said "this is true on the NG as well."

 

I had a CRJ pick off someone's hat once.  Definitely wasn't trying to set the GEs as a standard for picking people up.  Just noting that they were even more prone to it simply by moving that much more air.

I see your point. I was reading this thread on my phone and had to go back to the top of the forum to check which one it was. So it certainly wasn't clear.

 

 

This is correct, and that would be me.

Granted, I didn't do it from the flight deck, but as someone who's been the ground side of many a huffer start, I know how they're done:

 

Idle cart to warm

Connect hose

Once warm, (add extra hearing protection and) bring it up to operating power

Open valve when crew signals/requests

Crew starts requested engine (depends on aircraft type and SOP, but usually on the side opposite the huffer)

Crew signals disconnect

Close valve

Bring cart back to idle

Disconnect hose

Tow cart away, monitor temp, shut down once below placarded temp

 

Crew starts second engine after push using crossbleed.

It's very easy "in the sim" to think you can use all air sources with equal validity, but only those who actually work the ramp or fly the aircraft fully appreciate the practicalities. Another reason to do a crossbleed start would be if the APU bleed valve fails. That was a trick I've seen instructors use in the sim to get trainees to demonstrate the crossbleed start procedure.

It's fascinating how an off the cuff remark can generate so much discussion.  Thanks for all your input folks.  I read somewhere - can't find now - the procedure for the cross bleed start from one engine, and it stated that there is insufficient bleed air at idle, so the running engine must be taken above idle to get about 20PSI before the other engine can be started.  Hence my remark about running into the jetway.  My increase in power caused the aircraft to swing as I had forgotten to put the parking brake on.

That may be a typo but you would need at least 30 psi in the duct to be sure of a good start.

[scandinavian13 5,192]

It's very easy "in the sim" to think you can use all air sources with equal validity, but only those who actually work the ramp or fly the aircraft fully appreciate the practicalities. Another reason to do a crossbleed start would be if the APU bleed valve fails. That was a trick I've seen instructors use in the sim to get trainees to demonstrate the crossbleed start procedure.

 

Definitely.  I love the ability to sim that extra procedure.  Granted, it's not a CRJ, and it's not Mesa airlines*, but it's nice to sim a failed APU from time to time.

 

*Any time I saw Mesa (a YV tailnumber), I knew I'd need to start at least tracking the huffer down to know where to grab it when the crew told me "oh hey, our APU is inop" on arrival...

[JoeDiamond 67]

Yes - as mentioned: gravity and/or suction.  Additionally, I think the APU has a built in DC (electrical) pump, but using a tank pump is recommended.

 

Ours don't have any kind of DC pump for the APU.  With no AC power it's suction feed only.

[Spin737 102]

DC APU fuel pump is an option. Flown some with, some without. Mostly without.

[ahsmatt7 1,199]

To add on the crossbleed starts. Theres a specific carrier who's normal OPS are to do crossbleed starts on the CRJ 7 and 9s.

[Vagabondo 23]

I accidentally started the engines without the fuel pumps running ... successfully.  Is this properly modelled operation?  As the tanks are higher than the engines, I can imagine that this might be possible, though perhaps not above idle.

 

Same applies to the APU, but I watched a Real World video of a 737-800 startup, and sure enough, the pumps were not turned on prior to starting the APU.  That I find more odd as the APU must be at about the same level as the tanks.

As previously mentioned the engines and APU can get all they need by suction. IRL, a fuel left tank or left center pump is usually on for APU service life.

 

WRT to fuel suction feed by the engines, again IRL where the aircraft climbs trapped air in the fuel escapes and can cause cavitation, so it is pretty essential that at least one fuel pump is pressurizing the fuel line to each engine to prevent such cavitation. Once in the cruise, this risk is has usually passed and suction feed to the engines is, according to Boeing (I doubt anybody is will to try it), suffficient.

 

If PMDG has attempted to model this, serious hats off