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737NG Low Fuel

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737NG Low Fuel

Old 21st Jun 2008, 11:42
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737NG Low Fuel

These days with us all flying around on vapors! How confident can I be in committing to the destination airfield and commencing the approach with about 1.2 tons ie Amber 600 each side!

If I go around will the power plants continue to produce power for my next "no go around" approach with 300 kg each side?

Any ideas, experience welcome
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Old 21st Jun 2008, 12:38
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1) Yes
2) Probably, but you have erred.
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Old 21st Jun 2008, 13:47
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As far as I am aware, the aft main tank pumps should produce pressure almost down to empty, so you would still be in a situation where you had just under 30 minutes to dry tanks- a GO around to 1500' should not use a great deal. Actual unuseable fuel should be quite small, after all that is the aim of design! Carrying out the Low Fuel procedure should ensure you crash without asymmetric power (that's a joke!). I would have confidence that you could GA with 1200 and fly a circuit, though I might insist it was a short one!
I did Amber 760 recently. Not especially desirable, but at $150 a barrel, we are no longer tankers when not economical.
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Old 21st Jun 2008, 13:51
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BOAC - I hear what you are saying. However it is not uncommon these days. CRM is only 1800 in a lot of cases.

Thanks Rainbow and further info welcome. What about turbulence in these low fuel cases?
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Old 21st Jun 2008, 14:34
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Yes, D, but to go from 1800kg total to 600kg total would take some significant errors, don't you think? Perhaps you should be sure before you 'commit' that you will be able to land first time? Best not to get yourself into that 'statistical quagmire' you describe. We are beginning to go down the 'what if I get 2 emergencies' line and aviation is NOT designed to cater for that. As someone said elsewhere, if you are worrying yourself about that scenario, should you be flying at all?
However it is not uncommon these days.
- what is 'not uncommon'? 600 kg total, 1200kg total or what? A CMR of 1800kg should not get you anywhere near any of those.

The aft pump feed is only relevant during the g/a and accel. Once you either slow down or put the nose down for landing...................... In any case, providing they can find fuel in the tank, the motors will run without tank pump pressure.

Half of this problem (737NG) comes from the 'factory' (high) LOW setting at 907kg (discussed in another thread). Any yellow warning anywhere and people start twitching. 1810kg is a lot of fuel in reality. 1200kg is equivalent to 30 minutes holding. The Classic does not call for any drills until below 453kg on any side, and the NG burns less.

Last edited by BOAC; 21st Jun 2008 at 14:52.
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Old 21st Jun 2008, 15:18
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Our emergency fuel is 3000lbs and the final fuel(1500AFE to touchdown) is 300lbs.
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Old 21st Jun 2008, 15:44
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After a lengthy period of flying into airports where go-arounds have been few and far between, I have recently been operating out of an airfield where they are much more common, due to weather and airfield facilities. It has rather focussed my mind on this subject.

I am a bit sceptical about the statement that a go-around to 1500' should not use a great deal. I suppose it depends what you mean by a great deal. But on the last three occasions (with a 737) it was between 600 and 700 kilos. Given the need to declare an emergency at 1200 kilos, or rather more pertinently if you believe you will land with less than 1200 kilos, obviously there is not a lot of margin.

You would have to be pretty brave (some might say foolhardy) to take minimum fuel under these circumstances, as I am sure most if not all would agree. The more interesting question is how much is then enough? If a go-around is a distinct possibility I favour taking enough to try an approach and then have enough to divert and land with some options left.
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Old 21st Jun 2008, 16:13
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The structure of fuel reserves is usually of the order to fly to destination, go around and divert to alternate, plus Contingency (5% or 15 minutes holding), and land with 30 minutes left. As a planning minimum this is enough. As fuel becomes more expensive, you must tailor the cost of carrying any extra to your perceived risks on the day, as that extra fuel you carry every flight will hit the profit. You cannot justify this for the once in a blue moon event of a diversion through low fuel which may cost less than carrying extra fuel on average every flight. Remember, extra fuel mostly doesn't prevent that diversion. On most occasions when I have diverted, extra fuel merely delayed the inevitable.
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Old 21st Jun 2008, 17:08
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I am in complete agreement that extra fuel costs money. I suggest 3.5% per hour for the extra carried on the 737 is a typical figure. So taking the proverbial fag packet and rounding up, a thousand kilos extra on one of our average flights costs 40 kilos.

If there are no perceived risks, as you put it Rainboe, then there is no problem taking flight plan fuel. However your suggestion that needing extra is a once in a blue moon requirement is a bit short of the mark in my experience. On those occasions 50$ as against the thousands for a diversion is reasonable insurance.

Maybe you are a management pilot and have access to all the statistics (lies, damn lies, statistics etc.). But the statement that extra fuel merely delays the inevitable sounds a bit subjective.

There are definitely two churches out there as far as extra fuel is concerned. The minimalists are in the minority in our company judging by our remaining fuel figures. But obviously I cannot see those in your company.

I definitely agree fuel and cost can be saved in this area. I guess where we disagree is in the size of the cost / benefit equation, when also factoring in safety.
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Old 21st Jun 2008, 17:13
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Where have I seen all this before.....................?

Well, that was the LAST time
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Old 21st Jun 2008, 17:37
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Are you suggesting

1. Rainboe and I have not read a thread which stretched to 5 pages (unlikely at least in Rainboe's case)

2. The subject is not interesting (in which case why did you reply to the original post)

Last time I looked Danny was trying to encourage debate by professionals. Does this somehow not qualify?

As an aside, most times I have posted something on PPRuNe that I considered reasonably thought through, the thread then died. PPRuNe does seem to thrive on controversy. So I am trying to get with the flow!

Last edited by lederhosen; 21st Jun 2008 at 18:01.
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Old 21st Jun 2008, 18:09
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Mostly when I have diverted, I already had taken extra fuel. It did not change the outcome. last time I diverted, I held for over 2 hours at ARN waiting for fog to clear- it didn't and we wasted nearly 5 tonnes. We still returned to departure point having used up all our round trip fuel to get nowhere in 4 hours.

My estimation is that extra fuel, although nice to have, does not achieve half as much as people think. Personal opinions, but I get fed up with people wanting hundreds 'for Mum' to a non-delay destination on a good weather day. I used to do many long range flights from the Far East to UK with restricted minimum fuel. I never had a crisis. Ran low sometimes, but carrying extra on flights like that costs big time. I didn't feel additional was worth the cost.

Itmight be interesting to consider if you have diverted, had you already taken extra? Would carrying even more have saved the diversion? It's not as clear cut as 'carry extra=no diversion'.

This for unexpected problems of course
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Old 21st Jun 2008, 18:50
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If you have the luxury of flying a route regularly you can see how generous or not the flight plan fuel is, regular short cuts and better cruising levels for instance. We have an interesting situation, where the plans for our NGs are spot on, but the classics tend to need a bit extra. Anyone else have this problem?

At the end of the day I believe strongly in the red face test. If you can explain at the end of the day why you did what you did and not go red in the face explaining to your superiors, then things are OK.

I see the self evident target as landing at my destination as close to minimum diversion fuel as often as makes sense. I think landing with less is at least as bad as landing with more. In many cases landing with more reflects that you have saved fuel rather than wasted it!
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Old 21st Jun 2008, 18:58
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Carrying ABEFM does not guarantee you will not g/a with 600 a side.
Are you suggesting
1. Rainboe and I have not read a thread which stretched to 5 pages (unlikely at least in Rainboe's case)
- Yes, well should have
2. The subject is not interesting (in which case why did you reply to the original post)
- No. The SUBJECT was interesting. Hence the interest. ABEFM is not - here in this thread.

The thread is not "a closed subject" but there is this awful cemetary-like atmosphere of dead bodies being dug up again. What using 5 tonnes of fuel holding has to do with a low fuel g/a I cannot see.

To attempt to answer your question, Dogma, turbulence will be a factor, although the overall 'average' fuel available to the feed pipes will be sufficient as it sloshes around. Attitude and accel/decel are more crucial, hence the QRH.
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Old 21st Jun 2008, 19:20
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I get it now BOAC, you were declaring thread creep! Why did you not say so clearly in the first place?

Not particularly sure I agree, but it is your train set.
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Old 21st Jun 2008, 19:31
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We'll all stop flying around 'on vapours' after about three hull loss accidents with a couple of hundred dead each time. Anyone care to start a sweep on a date? My betting is that it won't be anytime soon.

Until then, the drill is simple: pumps on, crossfeed open, and mayday.
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Old 21st Jun 2008, 20:04
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Er......how many times has that happened? Do you expect it to? Why? If you carry fewer reserves, you must make your decision earlier. Extra fuel gives you extra thinking time. That optional luxury of extra thinking time is becoming increasingly expensive. Therefore you must take your decision earlier, and save the decision to take extra for when it is really necessary.
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Old 21st Jun 2008, 20:44
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As a non "operator", looking from the outside in, so to speak, I think the whole issue of low fuel levels and how you professionals "cope" and the difficulties that it brings with it actually comes down to experience.

Lots of experience.

The trouble is now, with foreshorted training designed to meet those training "targets" the flying hour/experience ratio is going the wrong way, IMO.

Please feel free to correct me as you feel fit!

glad rag.
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Old 21st Jun 2008, 20:58
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The biggest problem is when you follow mandatory procedures and are obliged to declare Mayday, PPRuNe gets hold of it and it is looked on as crew shrieking 'My God, we're in distress! Call out International Rescue, call out the Coastguard, call out everybody with a uniform with a Red Cross!' when it is simply a procedural thing, and compulsory. What is needed is a new word to convey 'low fuel situation- not about to die (but that possibility is not excluded).'

Won't be nearly so exciting in PPRuNe though.
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Old 21st Jun 2008, 23:08
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Thanks for the answers, suggestions and conjecture.

BOAC .. CMR = 1800 and you say that commencing the approach with a predicted landing fuel of 1200 = problem? ie you have committed and have breached no legal limit.

I want to know what the perceived wisdom is concerning arrival fuel. Personally I feel planning to arrive with a CMR of Low Fuel with NO mitigating factors is not correct or commensurate with good airmanship.

That said if you are up against it (Low Fuel), due enroute problems, should you have a gear, flap, slat, hyd, cont, brake problem then you need to be absolutely clear about your rapid course of action!
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