VNAV Flap Retraction / Acceleration Climb Gradient

[jon b 2,050]

On ‎09‎/‎03‎/‎2018 at 11:19 PM, berts said:

Thanks for the % figures Jon, although I am 100% certain you will notice a BIG difference in climb and acceleration performance between a lightweight and a heavyweight take-off on 4 or 3 engines!

I suppose having only two procedures in CARD (Packs on or off) as opposed to three reduces the risk of a mistake being made.  The 75 code for use in CARD with the APU Inlet Door being open does not give a correction figure in the notes I have. However, applying a 1,452 kgs penalty for the drag of the APU door being open seems like overkill to me.  As far as APU to Pack performance manual corrections is concerned, a 100kgs correction is (was?) applicable if the performance was Field Length limited and 400kgs if it is (was?) Climb (WAT) limited.

The TO1 and TO2 derates are intended for use on contaminated and VMCG limited runways so they are not normally included in any of the normal take-off summaries.  TO2 is intended for use on three engine ferries.

Bertie   

Quite right Bertie, there would be a big difference. I probably didn't write that well, what I was meaning was, could I tell 60% of the power was being used for climb or accelerating? no probably not !

You are right the TO-1 and 2 derates were  only used for contaminated runways or "special" occasions. Interestingly with the introduction of remote server calculations and complex performance applications like the Boeing on board performance tool used on an ipad on the flightdeck it is now not uncommon to see the use of TO-2 with an assumed temperature method thrust reduction. This results in the rather strange scenario of power actually being added at thrust reduction altitude as climb power is higher than take off power !

 

Cheers

Jon Bunting

[MattS 45]

11 hours ago, jon b said:

This results in the rather strange scenario of power actually being added at thrust reduction altitude as climb power is higher than take off power !

Skip to 21:25

 

[jon b 2,050]

There you go,...second gear !

[berts 97]

On 3/10/2018 at 10:18 PM, VHOJT said:

The only way I've managed in the sim to meet the at or above requirements out of OMDB with a full 744 is:  T/O thrust until 4000'.  At 1000', VNAV speed intervene and bug up to flap 10 retraction speed, then climb with T/O thrust and flap 10 until 4000'.  All the while I've really got no idea what gradient I've been averaging.  I am guessing meeting the at or above requirements would mean satisfying the gradient.

I've got myself in a muddle writing that.  Head is about to explode.

I think you've answered your own question.  If your head is about to explode it means it can't be done - and if you try so will all four engines !!!!

Bertie 

[VHOJT 177]

Gentlemen, especially Jon, Bertie and Simon, thanks very much for the time you have taken and the detailed answers you have given here.  What makes this forum so amazingly good is people like you.  I really appreciate it.

My apologies again for the late reply, I have just been flying from Australia to Dublin and have only just regained enough interest in aircraft after being in them for 30 hours to read about them haha.

Thanks again chaps :)

[Copper. 78]

On 08/03/2018 at 12:14 AM, downscc said:

I always use VNAV for 737/777 departures, my modification to the 744 procedure was based on two sources I had on BAW procedures.  Agree, there needs to be a pilot involved to take care of flaps and bug speed but it doesn't seem incorrect, but of course no one should be using V/S mode in this regime of flight. Lordy no.

Dan

If I recall, there used to be problems with arming vnav on the real ng with u10.8a fmc software loaded. As to the use of VS - it isn’t THAT bad. It’s a technique I use when flying at low gross weights, but at other times aswell. VS is a tool just as much as LVL CHG is - it just depends on appetite for risk. Vnav is the obvious front runner and VS the least - but VS and LVL CHG definitely useable.

Rudy

Airlines have internal departments that consider performance for pilots. This is typically the safest and efficient approach. Technological advances have improved this.

In practical terms - all engine and engine out cases are considered by them, as are other influencing parameters. They develop easy to follow all engine and engine out procedures for crew to follow and regulate weight (rtow) to be able to comply with any performance restrictions. These are manifested in tailored procedures I believe. In addition to these, there are tailored performance charts with gradients for specific airports and runways and their intersections. The opt will also determine performance based on requirements of the subsequent segments as programmed in the opt software.

By the time pilots become involved, they are generally performing checks to ensure everyone have done their bit. In case they haven’t, aforementioned mitigation strategy’s are used. I.e. request cancel alt rest, weight reduction etc.

in essence I’m saying the pilots use tools not available to us to determine performance. 

Edited April 20, 2018 by Copper.