View Full Version : Decisions for takeoff

21st Mar 2008, 13:05
1) I am not a pilot, but I was led to believe that when a pilot of a big commercial airliner looks up the RTOW for his departure runway out of the relevant performance manual, he could also get the FLEX Thrust setting and the Flap setting required for that runway.

I just wanted to clarify that an Airbus pilot, for example, can't simply select a flap setting for takeoff at his own discretion, he would use the flap setting stipulated in the booklet.

Or would he? Little bit confused...

2) I heard recently of a TCX flight that had to divert to a German airfield between somewhere sunny and Birmingham, because the pilots hadn't calculated enough fuel for the trip. I wanted to know, how the HELL that could ever happen - surely you've basically got the fuel required printed right there in front of you on the NAVLOG. If the Navlog was at fault, how could this happen?

Any help greatly appreciated


21st Mar 2008, 14:05

1. Actually we have a laptop to calculate the performance for take-off. The computer gives us flex, flap setting and speeds. You may select optimum flap and the computer will tell you which flap setting is best, or you may(for operational reasons) tell the computer which flap setting you would like to use. The important thing is that the speeds and flex corresponds to the chosen flap setting.

2. The running short of fuel happens incredibly easily. Airlines push us to carry mimimum fuel. The nav log typically allows less than 5 min contingency fuel. I have seen half this fuel used by excessive delay for take off after start. Then given that in busy airspace you probably won't get your flight level, you can very easily run into problems. The airline I fly for has had this happen a few times, especially routing through China(before they introduced more flight levels).

21st Mar 2008, 15:22
The nav log typically allows less than 5 min contingency fuel.

Did you mean "minutes" or "%"?


21st Mar 2008, 15:55
I guess it could be either. Ever since our lot moved from X% to Statistical Contigency we've seen some entertaining numbers. I was recently offered 5 minutes contingency for a sector >11 hrs..needless to say I declinded the offer..and needless to say we didn't burn any excess.....hey ho.

21st Mar 2008, 16:00
"The nav log typically allows less than 5 min contingency fuel. I have seen half this fuel used by excessive delay for take off after start."

That would mean you have taken off with less than min T/O fuel...

Nil further
21st Mar 2008, 16:05

You are incorrect (JAROPS/EUOPS) contingency fuel can be burnt at anytime after engine start.


21st Mar 2008, 16:21
Err, No, he's burnt (presumably) all his taxi fuel plus half his contingency..but that means he's still got half of contingency left...and all his "trip" fuel...OK to go by my rule book.

21st Mar 2008, 17:22
wiggy, spot on...........thanks

Contingency minimum on the A340 is 700kg.......enough for 5, maybe 6 minutes.

Ok, maybe I exaggerated a bit. Its not typical, but I have seen it several times and is 5 or 6 minutes not less than 5.

Another interesting point is that there is more of a problem on short flights due to lower contingency and there is less time to take fuel conservation steps en-route.

22nd Mar 2008, 16:02

To answer your first question about T/O performance, those airlines that do not use laptops do it exactly as you described. RTOW is calculated from the tables, then once you know the actual TOW you can get the engine derate (flex temperature) and the flap setting from the tables.

For safety reasons, sensible airlines will insist that both pilots calculate these figures independently, even to the point of insisting that the performance book is handed to the other pilot closed so he has to find the correct page himself.

22nd Mar 2008, 16:15
..or even option 3: send a request to a Mainframe via datalink..., and wait, fingers crossed, for the reply.

But even in that "high tech" method you get your colleague(s) to cross check what you've typed in by the way of data ( e.g. runway, wind, temperature, QNH) before pressing the "send" button...and you cross check the reply carefully as well....and if it all falls down it's back to the manuals.

Pilot Pete
22nd Mar 2008, 18:55
Or you both type it in separately to your individual laptops and cross check!:ok:


22nd Mar 2008, 21:55
:ok: I like that. We were told the reason for the datalink solution rather than laptops was certification issues, blah, blah..Personally I think my lot would rather spend a fortune on datalinking and having their teeth pulled without anaesthetic rather than "give" their pilots laptops......

Hand Solo
22nd Mar 2008, 23:26
And I'd rather they kept spending that fortune on datalinks rather than save the cash by forcing me to lug a brick heavy laptop all over the world. Company laptops are fine if you don't nightstop, change aircraft or want to take your own PC away with you.