ExpressJet Forum - View Single Post - N1 split in detent, ALT-TO1?

Mitch · 03-18-2008, 04:05 PM

The other day we were taking off and the first officer noted a 0.6% N1 difference between the two engines. Not just the actual N1, but the scheduled N1. Both engines were operating at the exact scheduled/commanded N1 in the detent, but they were 0.6% different from each other. Though not a major difference, and certainly not a safety concern at that level, it did get my curiosity going.

The FADECs matched themselves up with no problem after departure (shortly after setting CLB thrust,) but I had never noticed more than 0.1 or 0.2% difference before and thought the FADECs talked to each other to keep relatively equal thrust between sides.

I'm guessing that the FADECs were just getting slightly different data from somewhere and computing using that. It was windy, but not any more so than other days. There was no icing involved.

What is the maximum difference between sides that the FADECs are kosher with? No limitations come to mind, like I said, just curious.

(Don't have Vol 2 with me to look up everything handled on the inter-nacelle databus, and didn't immediately find anything on asymmetrical thrust margins in Vol 1.)

03-18-2008, 04:05 PM	#1 (permalink)
Mitch ATP Join Date: Feb 2005 Location: Shoulda stayed in San Diego Posts: 2,862	N1 split in detent, ALT-TO1? The other day we were taking off and the first officer noted a 0.6% N1 difference between the two engines. Not just the actual N1, but the scheduled N1. Both engines were operating at the exact scheduled/commanded N1 in the detent, but they were 0.6% different from each other. Though not a major difference, and certainly not a safety concern at that level, it did get my curiosity going. The FADECs matched themselves up with no problem after departure (shortly after setting CLB thrust,) but I had never noticed more than 0.1 or 0.2% difference before and thought the FADECs talked to each other to keep relatively equal thrust between sides. I'm guessing that the FADECs were just getting slightly different data from somewhere and computing using that. It was windy, but not any more so than other days. There was no icing involved. What is the maximum difference between sides that the FADECs are kosher with? No limitations come to mind, like I said, just curious. (Don't have Vol 2 with me to look up everything handled on the inter-nacelle databus, and didn't immediately find anything on asymmetrical thrust margins in Vol 1.) __________________ Warning: The unauthorized reproduction or distribution of this possibly copyrighted work could be illegal. Criminal copyright infringement, including infringement without monetary gain, is investigated by the FBI and is punishable by up to 5 years in federal prison and a fine of $250,000.