Why is there the requirement for switching on the Ignition in an Emergency Descent? Obviously airmanship wise it's never going to be a bad idea but anyone with more than that to add? Cheers CC1
For example, on a CFM56, it is detrimental to select ignition in almost any case according to CFM.... reason being it can detect a flame out more quickly than each spark on continuous; and if the spark is required due flameout there is a higher voltage available thus a stronger spark available in a fraction of a second due to not continually discharching the capacitors in the ignitor box. At the airline I work at it is SOP to select ignition on the CFMs in Emer descent... no idea why.
Probably because you are at idle thrust and don't know what conditions you may encounter on the way down. With all the chaos around, you may not be thinking (or have time to think) 'icing', so it seems like a good idea, regardless of type.
Just follow QRH. Otherwise we end up with a whole other virtual manual of opinions to muddy the waters. If you really think you have a great idea get your tech or training dept to ask the manufacturer.
ust follow QRH. Otherwise we end up with a whole other virtual manual of opinions to muddy the waters. If you really think you have a great idea get your tech or training dept to ask the manufacturer.
That is a pretty negative unhelpful comment to a perfectly reasonable question.
Ahem... missed the point of the original post. Apologies. Agree with MachE, though alot of modern engines have auto this and that so not as much a consideration as in the past.
For example, on a CFM56, it is detrimental to select ignition in almost any case according to CFM.... reason being it can detect a flame out more quickly than each spark on continuous; and if the spark is required due flameout there is a higher voltage available thus a stronger spark available in a fraction of a second due to not continually discharching the capacitors in the ignitor box
Would you mind posting your CFM reference for this post? Thanks.
I'm trying to find it for you, I had it in a presentation somewhere I am sure but no joy so far, I thought it was in a CFM ops seminar but can't see a reference now (unless I'm completely loosing the plot and thinking of the V2500). Any one else know?
Looking through the CFM seminar, if it detects any decel greater than expected on normal schedule (among other things) it will immediately engage dual ignition anyway.
@Tom Autoignition is available only on 737 - NG ( CFM 56 -7). On the classics CFM 56 -3 you don't have this feature ; in order to keep the commonality between CL and NG you have to put them on continous. Hope it helps
I had the impression that ignition is fairly important in a lot of circumstances on the V2500, given that you only have to sneeze and the ignition comes on.
What on earth is so hard to understand about that?
I know we descend at idle with no ignitors on every day, but are some of you some kind of self-appointed galactic test pilot who knows more about this than the manufacturer's test pilots do? Which TP school do you come from - do tell...
If such superior Test Pilot please speak up.
If not, kindly shut up and let the rest of us Professional pilots follow the checklist. Gobshyte fools.
Agree with QRH discussions but.... the question was posed as to why the procedure? That I interpret is a legitimate question to underrstand the reasoning behind it, rather than to challenge that it is wise to follow or not.
Somewhere in the vitrolic above are some excellent points that may or may not apply to the machine that you fly.
What on earth is so hard to understand about that?
I know we descend at idle with no ignitors on every day, but are some of you some kind of self-appointed galactic test pilot who knows more about this than the manufacturer's test pilots do? Which TP school do you come from - do tell...
If such superior Test Pilot please speak up.
If not, kindly shut up and let the rest of us Professional pilots follow the checklist. Gobshyte fools.
A great display of pure idiocy. I suggest you start running and see a specialist
Why is there the requirement for switching on the Ignition in an Emergency Descent? Obviously airmanship wise it's never going to be a bad idea but anyone with more than that to add?
I suspect it is simply a risk mitigation measure. An emergency descent is a busy time and descent through icing is likely and through unknown or unconsidered levels of precipitation is quite possible too.
Given the possible slow reaction by the crew due to workload and those potential changes in the outside environment, I think it should be judged an essential safety measure.
