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I was watching a documentary on aircraft incidents which mentioned that the 737 does not have the facility to dump fuel. Instead they're required to fly in circles to burn off excess fuel in an emergency.

It strikes me as a little odd, as someone without detailed knowledge of the 737-series' fuel systems, that the world's most popular passenger jet doesn't have this capability.

What was the design consideration/reasoning for this?

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    $\begingroup$ Possibly part of why it's so popular is that it's cheaper, due in part to not having a fuel-dump system? $\endgroup$ – Sean May 21 '18 at 17:12
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TesterMen Tester provided some very good information which I think requires a bit of explanation. The older version of the regulation seems to require fuel dump capability if MTOW is more than 105 percent of MLW. None of the 737 versions have weight limits under this requirement, so based on that regulation, it seems like fuel dump would be required. But as the Boeing info shows, none of the 737 versions have fuel dump capability.

That regulation was amended in 1968 to allow a plane to not have a fuel dump system as long as it can meet certain performance requirements. The current version of the regulation includes this as well.

However, this does not explain why the 737-100/200, which were certified before that amendment, don't have fuel dump capability, when the MTOW listed by the Boeing info above are 108% and 112% of the MLW.

The explanation is that the original versions of the aircraft had lower MTOW, which met the 105% rule. Newer engines allowed the MTOW to be increased, but as rbp mentioned, MLW is based on landing gear and structural limits, so it did not change. The FAA amended the regulation with the required performance option to allow the higher MTOW without requiring fuel dump capability. Also, as explained in answers to this related question, planes can land over MLW, there just may be required inspections.

Note that the similar-sized A320 family does not have fuel dump capability either. Smaller planes usually don't end up with the kind of fuel capacity and takeoff weights that justify a system to dump fuel.

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    $\begingroup$ SU-1492 has made an emergency landing several days ago. Landing was successful, but passengers burned in 13000 liters of kerosene. This is the main reason not to fly on planes without fuel dumping system. A320, 737, Embraer, Douglas, superjet, etc -> do not fly on it. Use A340-A380, 747-787. $\endgroup$ – puchu May 8 at 8:59
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    $\begingroup$ @puchu there's a whole lot more to that crash than simply having fuel onboard... $\endgroup$ – SnakeDoc May 21 at 22:57
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    $\begingroup$ @puchu it does matter, things like the airport fire crew not rolling out until after the plane was on fire, and without foam even loaded!... passengers stopping to get their luggage instead of just evacuating, or even the investigation into whether or not the pilot was properly trained to handle DIRECT flight law and possibly have caused the landing gear to fail by bouncing on all 3 wheels multiple times even though there's no reported damages to flight systems. A smaller amount of fuel on board would have still burned and still killed people under the same conditions. $\endgroup$ – SnakeDoc May 22 at 16:13
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    $\begingroup$ @puchu a fuel dump would not have helped here. Dumping fuel takes time. Time not available when you make an emergency landing. Having a dump fuel system is also a source of failures, when it is inadvertently activated mid flight. Has lead to hull loss before. Your comment is very misleading. $\endgroup$ – Antzi Aug 23 at 2:03
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    $\begingroup$ Look, I'm glad you found an exemple where dumping fuel might have helped, but it would be ridiculous to fly only jumbos because of this sole reason: It has not statistical meaningful effect on your survival rate. $\endgroup$ – Antzi Aug 25 at 8:07
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Sec. 25.1001 Fuel jettisoning system.

(a) If the maximum takeoff weight is more than 105 percent of the maximum landing weight, there must be a fuel jettisoning system able to jettison enough fuel to bring the takeoff weight down to the maximum landing weight. The average rate of fuel jettisoning must be at least 1 percent of the maximum takeoff weight per minute, except that the time required to jettison the fuel need not be less than 10 minutes. This must be shown at maximum takeoff weight, with flaps and landing gear up, and in-- {balance deleted for brevity]"

version of 25.1001 effective on 02/01/1965.

It seems that the 737 and also the 757 fit in that Regulation.

2 very nice Regulation Documents

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  • $\begingroup$ I don't have precise figures, but the 737 MTOW is indeed only a bit higher than the MLW. In any case, overweight landings are not a particularly big deal in most cases - just an extra engineering inspection is required. $\endgroup$ – Ben Oct 29 '14 at 9:01
  • $\begingroup$ i'll just throw the comment in here that MLW is calculated by the strength of the landing gear. $\endgroup$ – rbp Oct 29 '14 at 13:07
  • $\begingroup$ This regulation is very bad. Planes with full tanks should be able to make an emergency landing. Emergency landing includes tanks destruction. But sea of kerosene will explode and kill everyone. See SU-1492 accident. $\endgroup$ – puchu May 8 at 9:06
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    $\begingroup$ @puchu: "Includes tanks destruction" is a crash, not a landing. $\endgroup$ – Sean Aug 21 at 1:40

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