n901wa wrote:The Eng uses Bleed Air to turn the starter. If you run the packs ( They run on Bleed Air too) You don't have enough air pressure to get the starter to turn fast enough to get the eng turning fast enough to add fuel to the engine, so it can start. Not sure on the 787 since that uses Electric. Hope that helps
Max Q wrote:I believe some aircraft, perhaps the 747 can leave one pack on during engine start and we never tried it but
theoretically we could do the same on the 727 by re configuring the #2 engine bleeds
zeke wrote:You don’t touch the packs when starting an Airbus normally.
RetiredWeasel wrote:Max Q wrote:I believe some aircraft, perhaps the 747 can leave one pack on during engine start and we never tried it but
theoretically we could do the same on the 727 by re configuring the #2 engine bleeds
Yes you could, but not for the first engine started at least according to our ops. I posted before, after getting one started, you could isolate the pneumatic duct on that side so the APU supplied air only to the opposite side to start it's engines . The one engine running would then provide bleed air to run the one pack on its side of the ducting. The one engine and one pack provided a little relief while starting in a very hot environment. It got some air moving at least. That technique was used infrequently.
Max Q wrote:RetiredWeasel wrote:Max Q wrote:I believe some aircraft, perhaps the 747 can leave one pack on during engine start and we never tried it but
theoretically we could do the same on the 727 by re configuring the #2 engine bleeds
Yes you could, but not for the first engine started at least according to our ops. I posted before, after getting one started, you could isolate the pneumatic duct on that side so the APU supplied air only to the opposite side to start it's engines . The one engine running would then provide bleed air to run the one pack on its side of the ducting. The one engine and one pack provided a little relief while starting in a very hot environment. It got some air moving at least. That technique was used infrequently.
Thanks for that RW,
Interesting, I though I’d heard that before. Theoretically you could do the same on the 727 after starting one
It wasn’t approved so I never tried it
GalaxyFlyer wrote:I hope the OP isn’t a pilot of airliners. Appalling lack of mechanical sense, if so.
GalaxyFlyer wrote:I hope the OP isn’t a pilot of airliners. Appalling lack of mechanical sense, if so.
Tristarsteve wrote:The Tristar had a PT6 engine for its APU. It produced bleed air all the time, but if there was no demand, or the APU bleed valve was closed, there was a surge valve on the APU that opened and blew all the excess air very noisily overboard. So we tried to not open the surge valve by selecting the relevant pack on as the the start valve closed on the engine. With two cross bleed valves and everything manually controlled on the FE panel it was possible.
speedbird52 wrote:GalaxyFlyer wrote:I hope the OP isn’t a pilot of airliners. Appalling lack of mechanical sense, if so.
I clicked on this thread just to post this. The reason why is literally in the FCOM. If you can't be assed to read that (and somehow pass all your tests...) this is something that can be answered with 5 seconds of Googling. The only airliners I have ever flown are virtual airliners, and even I managed to learn why just by reading the manual.
n901wa wrote:The Eng uses Bleed Air to turn the starter. If you run the packs ( They run on Bleed Air too) You don't have enough air pressure to get the starter to turn fast enough to get the eng turning fast enough to add fuel to the engine, so it can start. Not sure on the 787 since that uses Electric. Hope that helps
thepinkmachine wrote:I once forgot to switch off the bleeds/packs before engine start on EMB145. The result was a hung start (or 2, I don’t remember).
We only could start it when we figured out the reason...