# How much distance it would take for a 747 type aircraft to stop without breaks **URL:** \ **Category:** Factual Questions\ **Created:** [January 5, 2015, 2:14pm UTC](https://boards.straightdope.com/t/how-much-distance-it-would-take-for-a-747-type-aircraft-to-stop-without-breaks/709033 "2015-01-05T14:14:02Z")\ **Posts on this page:** 5\ **Page:** 2
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [January 5, 2015, 6:06pm UTC](https://boards.straightdope.com/t/how-much-distance-it-would-take-for-a-747-type-aircraft-to-stop-without-breaks/709033/21 "2015-01-05T18:06:00Z")
> [@Duckster](#): > > Fair comment. But can you safely land a fully loaded 747 in an emergency just after takeoff? The 747 that declared an emergency last week leaving the UK for Las Vegas had to circle for several hours to burn fuel before it could land. > > So can the landing gear take a MTOW for landing? And what are the risks when the plane is full of fuel during an emergency landing? It’s possible, but best not to if you can avoid it; doing so means a higher speed at touchdown (due to higher stall speed because of high weight) and a longer decel (due to higher speed and higher mass), and also means that a mistake when flaring is more likely to overload the landing gear. In the case you mentioned (hadn’t heard of it), apparently they apparently didn’t need to land Right This Minute, so it was safer to burn off a bunch of fuel and lighten their load before touchdown. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [January 5, 2015, 8:39pm UTC](https://boards.straightdope.com/t/how-much-distance-it-would-take-for-a-747-type-aircraft-to-stop-without-breaks/709033/22 "2015-01-05T20:39:29Z")
> [@Duckster](#): > > Fair comment. But can you safely land a fully loaded 747 in an emergency just after takeoff? The 747 that declared an emergency last week leaving the UK for Las Vegas had to circle for several hours to burn fuel before it could land. > > So can the landing gear take a MTOW for landing? And what are the risks when the plane is full of fuel during an emergency landing? \*\*Machine Elf \*\*nailed it. Here’s some more detail / background … There is a regulated max landing weight _for normal day to day use_. And it’s significantly less than max regulated takeoff weight. But we can physically safely land at regulated full-up max takeoff weight. And there’s a regulatory special case for doing so _when you have a darn good reason_ as Steve Martin might have said. So-called “overweight landings” then require a maintenance inspection to ensure nothing was overstressed. And we need not to prang it on, lest something be overstressed & perhaps break. Autoland systems aren’t certified for those weights, so it has to be done manually. Brakes and tires (and runways really) are sized for landing at the normal landing weights. Since Kinetic Energy goes up at the square of the speed, an extra 20% of landing speed to offset the extra weight means dissipating an extra 44% of KE. That excess eats into the margins that give brakes and tires their economic lifespans. Each flap setting has a maximum speed limit that if exceeded may cause overstress. Exceeding a limit also requires a maintenance inspection and perhaps parts replacement, or something may even bend or break in flight which would be Very Bad. The slowest you can fly at each flap setting before stalling goes up as you get heavier. For very heavyweight situations you can get into a near Catch-22 where your max safe speed for a particular flap setting is only a couple knots above your min speed for the same configuration. In gusty conditions you’re essentially assured of violating one limit or the other. So landing overweight is \*not \*a white-knuckle, “Gosh Jim I hope she holds together” scenario. But it \*is \*operating in the area where we can spend a lot of employer money and create a multi-hour delay or flight cancellation with less than near-perfect handling. So it’s something to be entered into soberly with some respect. Any time you’re considering landing overweight, the situation is already non-standard. Something has gone wrong. If that something also affects stopping capability adversely, but doesn’t much interfere with flying, and is unlikely to deteriorate further over time, you may have a good reason to circle to burn or dump fuel rather than land overweight \*and \*with degraded stopping. Much to many folks’ surprise, reducing the supply of fuel for a potential post-landing fire has just about zero to do with the decision tree. It’s all about weight & stopping distance & not burning up brakes or ending up off the far end of the available runway. ---
**Author:** ![MikeS](https://avatars.discourse-cdn.com/v4/letter/m/919ad9/32.png) [@MikeS](https://boards.straightdope.com/u/MikeS)\ **Post date:** [January 5, 2015, 10:28pm UTC](https://boards.straightdope.com/t/how-much-distance-it-would-take-for-a-747-type-aircraft-to-stop-without-breaks/709033/23 "2015-01-05T22:28:45Z")
> [@AK84](#): > > How far Did it take for that 2001 plane which leaked fuel and glided to stop? > [@JerrySTL](#): > > Good question. However most aircraft have emergency brake accumulators to actuate the brakes a few times. If they applied the brakes and held them, this could have slowed the aircraft. Antil-lock brakes would have to be off. Looking at p. 11 of the [report on Air Transat 236 (PDF)](http://www.fss.aero/accident-reports/dvdfiles/PT/2001-08-24-PT.pdf), it was in fact the emergency brake accumulators that saved them: > [@](#): > > The aircraft first contacted the runway at 1 050 feet from threshold and then bounced for 1 650 feet prior to the second and last touch down. > > … > > Due to the engines-out condition, the landing was conducted without the brake anti-skid and normal breaking systems. Because the emergency brake accumulator only provides for a limited amount of brake applications, full braking was applied and retained at the second touch down, resulting in the main wheels locking up. The tires quickly abraded and deflated at a point between about 300 and 450 feet beyond the second and final touch down. The segments of the main wheels contacting the pavement were worn down to the bearing journals, the left, rear, inboard wheel detached from the axle. Total stopping distance after the second touchdown, with the wheels locked and rapidly eroding away, was about 4800 feet. ---
**Author:** ![Duckster](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/duckster/32/1244_2.png) [@Duckster](https://boards.straightdope.com/u/Duckster)\ **Post date:** [January 5, 2015, 10:39pm UTC](https://boards.straightdope.com/t/how-much-distance-it-would-take-for-a-747-type-aircraft-to-stop-without-breaks/709033/24 "2015-01-05T22:39:28Z")
Thanks **LSLGuy** , and **Machine Elf.** ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [January 6, 2015, 12:58pm UTC](https://boards.straightdope.com/t/how-much-distance-it-would-take-for-a-747-type-aircraft-to-stop-without-breaks/709033/25 "2015-01-06T12:58:25Z")
> [@MikeS](#): > > …with the wheels locked and rapidly eroding away, was about 4800 feet. Sweet photo of main gear: see Figure 2, page 11 at your link. :eek: [Previous page](https://boards.straightdope.com/t/how-much-distance-it-would-take-for-a-747-type-aircraft-to-stop-without-breaks/709033.md?page=1)