LOSS OF SYSTEM B - Fuel burn

[B737NG_Pilot]

As per the QRH the drag penalty with the leading edge devices extended may make it impossible to reach an alternate field.

How do we know, the fuel penalty/burn rate, with the LE devices extended? This is an important factor to decide whether to hold, or divert.

[latetonite]

Add roughly 10%.

[Mozella]

How do we know, the fuel penalty/burn rate, with the LE devices extended? This is an important factor to decide whether to hold, or divert.

I've never flown the 737 but if I wanted to know the fuel burn rate I'd take a look at the fuel flow gauges, especially if the aircraft configuration was not normal.

Then, if there was a question of range and/or endurance, I'd do a few calculations involving time/speed/distance. Back in my day they used to call it navigation.

[latetonite]

In my commercial pilot days, I would take my TAS, multiply it by the amount of fuel on board, and devide it all by the FF.
That would give me my ultimate range.

Be aware: the minimimum reserve according to your SOP's were not included.

An Aristo Computer showed the results in no time. Not sure if a todays iPad does the job.

[flying apple]

just go to the engine page and look at the fuel flow

[RAT 5]

As per the QRH the drag penalty with the leading edge devices extended may make it impossible to reach an alternate field.

When you have a HYD B system failure and need to extend the flaps & LED's using the alternative method I would suggest you only need to do this once setting up for an approach to land. Thus, when going through the decision making process, you should be very wary of your fuel state. This might influence your choice of landing field; i.e. one where you will NOT need to make a diversion if fuel is low. Once you are ready for the approach you can now lower the LED's and the extra drag etc should not present a problem. If you've fuel aplenty then you can be very generous with your extra fuel flow allowance, but i'd suggest it will be less than 'gear down ferry' inflight data; and that is available in the manuals.

[B737900er]

Or you could use "fuel freeze" if your flying a sim :ok:

[BOAC]

There is, of course, a supposed way to get them up again, but cojones required.:)

[Jwscud]

As there is, one hears, a way to release the parking brake in flight should you "accidentally" set it in a spirit of inquiry.

I hear it involves pulling circuit breakers in a particular order then taking the MEL to insert down one's trousers in preparation for the inevitable trip to see the Chief Pilot.

[RAT 5]

There is, of course, a supposed way to get them up again, but cojones required.

That would be the "depressurise the SBY system and apply suitable -ve G" method, of course.

The definition of skill full airman comes to mind. If you put them out under the correct conditions why would you want to enter the 'smart arse of the month' contest. I assume ardua astraeus was tongue cheek, hopefully.

[BOAC]

That would be the "depressurise the SBY system and apply suitable -ve G" method, of course.
....er no, actually, and I have not found a way to move LEDs in with negative g as you presumbaly have?

[Pastor of Muppets]

Well do tell.
As with the "run pwr" cb for gear retraction. It may never get used but it just may.....

[BOAC]

Cannot recall the detail now, but it was from a BA trainer on a sim check who was adamant that if you close No 2 with alt flap at less than 15, alt flap switch 'OFF', flap lever 'UP', the LEDs will retract on the PTU. I cannot remember the detail now - it was many years ago. I never tried it. Something for spare time in the sim? I can't remember why you had to close No2 - I would have thought the PTU would have worked anyway in that config.

[Pastor of Muppets]

Interesting. I wonder if switching off the B sys EDP would do the same thing?
Thanks BOAC.

[BOAC]

If you mean 'Engine Driven Pump' I'm not sure how you do that since you cannot stop it running unless you close down the donk.

[latetonite]

The PTU would operate, unless it was inhibited by operating the Alt Flaps up/dwn control switch.

[Aluminium shuffler]

If the B system is available, then why would you be using the alternate flap system? So the idea of switching off the engine driven pump to trigger the PTU to retract the LEDs under the guise of autoslat retraction would not be logical. Also, the autoslats work between "flaps not up" ans flap 15, ie when the LEDs are in the "extend" rather than "full extend" position, so trying to trigger the autoslat retraction logic would only return the slats to the mid position and do nothing to the Kruger flaps.

I also suspect more than a 10% increase in fuel burn with the LEDs extended.

As suggested, looking at the fuel consumption at 220kts and thus your endurance and then calculating range will tell you what alternates are viable. It just takes some basic arithmetic and doesn't need an FMC, though it'd save a bit of effort if the FMC had a feature to do this for you.

[Breakthesilence]

Find a good Attitude / Thrust setting table of the airplane you fly.

Usually, it contains Attitude / N1% / IAS / Configuration and FUEL FLOW data.

Just take a look at the Fuel Flow with Flaps XX. A good example in the following great document (B737 Classic):

http://www.b737mrg.net/downloads/b737mrg_powersettings.pdf

Flaps 5 Level Flight is 1200 Kg/hr while the Clean one is 1000. So It is 20% penalty.

Gear Down Flaps 15 is 1500 Kg, so 50%. I can assume Flaps 10 could be 30-35% due to the LED going to Full Extend.

It is a good quick hint in a busy situation. If you have time just cross check it with the Actual Fuel Flow or....at the next flight make some tests :ok:

[latetonite]

Why would you do that if the actual FF is right in front of you?