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Jambo Buana
10th Feb 2002, 18:12
Does anyone have technical info regarding the 'bump'? Does it revert to 26K automatically at 1500'agl? How much more ALT capability might you expect from a 27K engine over a 26K one? Are there only two derates available through the FMC? ie if you have 27K engines, only 26K and 24K are derate options? If you were buying an NG with an option for 27K full rated engines or Bump engines which would you choose and why?. .One last question, has anyone had any experience with the CFM 56-3 DAC, rather than the SAC, on the NG? Any good or not?

PETIGRAM
10th Feb 2002, 22:59
Jambo Buana:

“Does anyone have technical info regarding the 'bump'? Does it revert to 26K automatically at 1500'agl? How much more ALT capability might you expect from a 27K engine over a 26K one? Are there only two derates available through the FMC? ie if you have 27K engines, only 26K and 24K are derate options? If you were buying an NG with an option for 27K full rated engines or Bump engines which would you choose and why?. .One last question, has anyone had any experience with the CFM 56-3 DAC, rather than the SAC, on the NG? Any good or not?”

I fly an NG with a 24>26 K Bump and I’m pretty sure they work the same. Yes – it will automatically revert out of the Bump. “How much more ALT capability might you expect from a 27K engine” – if your asking about performance, it’s pretty good with a Bump. 24>26 K yields about an extra 10,000 Lbs. for Take Off (when you’re field length limited)!! I would suspect about half that for a 26>27 K Bump. Still are 2 Derates available on ours – but I don’t know how using the derates and the Bump would benefit you? The Bump is great if you need it – if you’re only going to fly out of long runways – and you’re sure of that – why add to the cost However, if there is a possibility of going into short fields with a heavy airplane, it would really come in handy. I heard some bad things about the DAC turbine sections – I honestly can’t remember what it was – but something about a required inspection or other problem that wasn’t present on the SAC. You’ll have to check further on this last point yourself.

Let me know if you are looking for a pilot for your new airplane.

Good luck,

Grew

Jambo Buana
11th Feb 2002, 03:00
We would definitely only require the bump for T/O performance, be it FLL or Obstacle limited. The added CRZ ALT capability would be something I'm interested in. I do not believe 26K compared to 27K will really make a significant difference. The difference I am trying to work out is basically, will we save more engine life with an occasional bump required T/O at 27K and still be able to assume temp reduce to 22K 50 degrees circa. Or is there significant savings in having a 27K fully rated engine which will take us higher (short haul operator bare in mind) but only be able to reduce to 24K @ 50 degrees? Thereby loosing a little EGT margin type saving.. .I know I have access to our Boeing field rep, but am doing a little on the job homework in the mean time.. .Your reply is appreciated. Do you really want to work in Blighty? HAWAII !!! Come on