Hemispheres From United States of America, joined May 2004, 85 posts, RR: 0 Posted (11 years 2 weeks 5 days 12 hours ago) and read 3374 times:
I've always wondered this but was too dumb to ask. Why is the engine pylon for the #1 engine different than the rest. It's missing the distinctive hump toward the front of the engine. Anyone know the purpose? (enlarge the first pic, you can see what I mean better)
Jetstar From United States of America, joined May 2003, 1737 posts, RR: 10
Reply 2, posted (11 years 2 weeks 5 days 11 hours ago) and read 3342 times:
The foward part of the engine pylons for #2, 3 & 4 have the turbo compressors needed for the aircraft cabin pressurization system, Engine #1 did not have the compressor.
In the early jet airplane days, the FAA did not allow engine bleed air to be used for cabin pressurization, they had to use outside air. The turbo compressors used engine bleed air to drive a pump the compressed the outside air and pumped it into the cabin.
Nowadays engine bleed air is now used for direct cabin pressurization.