Welcome to Flightinfo.com

  • Register now and join the discussion
  • Friendliest aviation Ccmmunity on the web
  • Modern site for PC's, Phones, Tablets - no 3rd party apps required
  • Ask questions, help others, promote aviation
  • Share the passion for aviation
  • Invite everyone to Flightinfo.com and let's have fun

ERJ-135 question

Welcome to Flightinfo.com

  • Register now and join the discussion
  • Modern secure site, no 3rd party apps required
  • Invite your friends
  • Share the passion of aviation
  • Friendliest aviation community on the web


Well-known member
Oct 12, 2004
Rode an AE 135 today... sitting in 8A, 1) the flow of air was incredibly loud coming out the floor vents, and 2) the airflow would cycle on, then off, then on, off, etc... corresponding to the APU cycling high and low. Normal pack operation or crappy APU bleed valve? Thx.
It might be that ground air was still hooked up. It does not always play well until the ground air is disconnected.

No ground air, the APU was running while we were boarding.. in fact this cycling of airflow continued as we pushed back. Really loud cycling, and every time it would cycle to high flow, sounded like the APU was cranking to a higher RPM as well. Kind of sounded like a jet engine going from idle to full power and back every time the air flow cycled.

It stopped when the packs were turned off for engine start. I've never heard it before, that's why I ask.
It just does that sometimes. I think it has to do with the demand that the packs are putting on for bleed air. The temperature might be affecting that demand variable. Like I said, it seems to me that it happens more often when the ground air is hooked up, but that might be my perception.

Sometimes resetting the packs makes it go away. Sometimes going to one pack helps.

pack 1 will do that when you are running both on the ground. Normal type operation
Sounds like surging ACMs(Air cycle Machines). They sometimes do that. Nothing to do with the APU. But on engine start a technique people use is turning off the #1 pack prior to turning the engine over to prevent a ugly pressure bump. But normally with both packs running and you start a engine, the #1 pack kicks off.​
Thanks for the responses. I've never heard the packs being that loud in the cabin - loud enough that the automated safety briefing could not even be heard.

Otherwise, no complaints... thanks for getting me to and from work, Eagle!
They don't call 'em the Whistling Sh**cans of Death for nothin'! Don't worry, as soon as it takes off, the airframe noise will drown out the ACM noise...

Latest resources