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777 stops in a dime - is this realistic?


paulyg123

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I was re-enacting the 737-700 that landed at the wrong airport and I also stopped with 500 ft left - pretty realistic.  So it took about 3,000 ft to stop a 737 with hard braking on a dry runway. - no winds)

 

I tried the same on the 777 and I was able to stop in 2,200 ft.  Can a 777 with a ZFW of 408,000 lbs really stop safely in 2,200 ft?  That seems to be my typical stopping distance on most of my landings.  (or is something wrong with my set up.)

 

BTW,  anyone else land at a wrong airport?  I got 1 under my belt.

Paul Gugliotta

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I was re-enacting the 737-700 that landed at the wrong airport and I also stopped with 500 ft left - pretty realistic.  So it took about 3,000 ft to stop a 737 with hard braking on a dry runway. - no winds)

 

I tried the same on the 777 and I was able to stop in 2,200 ft.  Can a 777 with a ZFW of 408,000 lbs really stop safely in 2,200 ft?  That seems to be my typical stopping distance on most of my landings.  (or is something wrong with my set up.)

 

BTW,  anyone else land at a wrong airport?  I got 1 under my belt.

Trying to find specs on this, none yet so far. I would think the B777 can stop faster than a 737 because of technology. The B777 has a lot of rubber on the ground and huge reverse thrusters. Yes the B777 has more weight but it also has more technology behind it.

 

Something to check out in this matter, click here. More

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and huge reverse thrusters.

 

777 does not have reverse thrusters. It does have thrust reversers.

 

 

 

Anyway the question is, how heavy are you when you land? The 777 is meant to be able to stop when heavily laden, of course when it is light it will stop fast.

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I'd assume that the insane acceleration at low weights transforms into equally insane deceleration at even lower weights (fuel burn).

 

Thinking of the size and number of wheels ("rubber on the ground") - it's plausible to me at least.

 

(Autobrakes, of course, have pre-defined deceleration rates, independent from weight.)

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Check out page PI-QRH.11.1 of the QRH. It shows that with a landing weight of 200,000 kg (about 441,000 lbs), Flaps 30, and Autobrake 1, the 777 will stop in 2,060 ft on a dry runway (plus/minus any corrections for environmental factors).

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Check out page PI-QRH.11.1 of the QRH. It shows that with a landing weight of 200,000 kg (about 441,000 lbs), Flaps 30, and Autobrake 1, the 777 will stop in 2,060 ft on a dry runway (plus/minus any corrections for environmental factors).

 

You do realize the distances in that QRH are in meters and not feet. 

 

At that weight, flap setting and autobrake 1, it is 2060 meters (6758 feet).

 

And contrary to what some have claimed here, autobrake 1 is not used by the any of the major operators. Why? because they know that it will lead to brake modulation and uneven wear compared to AB2 and AB3. 

 

The FCOM/FCTM state exactly that.

 

From my friend who flies for the worlds biggest 777 operator: When landing light enough to only need AB1 or is planning a turnoff at the end of a long runway, he will simply select AB2, and click them off at 100kts and gradually apply manual braking.

 

On the 200/ER/LR ~80% the landings are done with AB2.

On the 300/ER ~80% of the landings are done with AB3.

 

Of course the exception being NCL and BHX in the rain where AB4 and AB MAX are often necessary.

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According to the factory brochure, the 777 series is now available with ABS disc brakes.

 

When equipped with that option, the vehicle can stop on a quarter.  They are still working on stopping on a dime.

 

Opps, that was for a 2014 Camaro 2SS (shown).  Wrong brochure.

 

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Last 2 pages - you will note that the shortest landing runway length required is 3,700'.  There is a regulation that requires the airplane to be able to stop in 60% of the effective runway length to be dispatched to an airport.

 

http://www.boeing.com/assets/pdf/commercial/airports/acaps/7772sec3.pdf

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You do realize the distances in that QRH are in meters and not feet. 

Oops, my bad. Being American has its disadvantages leading to erroneous assumptions. Still, using Max Manual braking at KPLK would still leave you about 560 feet to spare (out of a 3,449 feet available) which is more than the Southwest 737 had left. However you slice it, the 777 does have good stopping power.

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There's an interesting video here of Boeing's Rejected Takeoff certification test. The quality isn't that great, but you can see clearly enough. A 777-200 at the Maximum Takeoff Weight of 288 tonnes (288 000 kg, or 545 000 lb) was accelerated to a V1 speed of 210 mph/183 Kt, at which point maximum brakes were applied. Despite using badly-worn brakes, the aircraft stopped in 4000 ft. Since the weight and speed are both quite a bit higher than they would be for a normal landing, that's pretty impressive, as are the glowing carbon disc brakes at 3000° C.

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You know I have wondered about this myself numerous times and was waiting to see if anyone else noticed it. I did a rough check by picking an airport (pay ware scenery to get the most accurate distances) and used the charts, measured the distance from threshold to a taxiway, then looked in the FCOM, the chart that says "auto brake landing distances" picked calm wind, picked one of the speeds listed to the corresponding distance closest to what I measured on the chart, and surprisingly, at least for auto brake 2 which is what I tested, the atopic distance seems to be correct.

 

Btw reverse thrust doesn't have any effect on braking distance and weight should not affect stopping distance DIRECTLY (the increase distance would be due to the increase in approach speed caused by the increase in weight) as the auto brake are meant to achieve a RATE of deceleration.

 

I guess one of the reasons why I think it stops too quick is because I'm used to the 737 where you have 4 wheels braking vs 12 on the 777.

 

Still I would like to do more accurate tests and post some results doea anyone know of a utility for fsx that measures distances on the ground?

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Btw reverse thrust doesn't have any effect on braking distance and weight should not affect stopping distance DIRECTLY (the increase distance would be due to the increase in approach speed caused by the increase in weight) as the auto brake are meant to achieve a RATE of deceleration.

 

This is right when talking about autobrakes, but both of these have an effect when using maximum manual braking or RTO braking.

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You know I have wondered about this myself numerous times and was waiting to see if anyone else noticed it. I did a rough check by picking an airport (pay ware scenery to get the most accurate distances) and used the charts, measured the distance from threshold to a taxiway, then looked in the FCOM, the chart that says "auto brake landing distances" picked calm wind, picked one of the speeds listed to the corresponding distance closest to what I measured on the chart, and surprisingly, at least for auto brake 2 which is what I tested, the atopic distance seems to be correct.

 

Btw reverse thrust doesn't have any effect on braking distance and weight should not affect stopping distance DIRECTLY (the increase distance would be due to the increase in approach speed caused by the increase in weight) as the auto brake are meant to achieve a RATE of deceleration.

 

I guess one of the reasons why I think it stops too quick is because I'm used to the 737 where you have 4 wheels braking vs 12 on the 777.

 

Still I would like to do more accurate tests and post some results doea anyone know of a utility for fsx that measures distances on the ground?

Something to bear in mind: The 737 often has higher approach VREF speed than the 777! The -200LR with her big wings usually after a very long flight is pretty light, hence it is often at around 137kt VREF. 737NG can be in the 140-150 range. This will also have an impact on stopping distance. The aerodynamic braking alone on the 777 is impressive if you hold the nosewheel off the ground for a bit longer than usual.

 

RE differing weights, look at it this way, what percentage difference between max takeoff and max landing weights between the two? The 777 has a much greater percentile difference between its max landing and max takeoff. BUT, its brakes need to stop it at max takeoff... see what I am implying?

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As I always say, I'm not quite sure people realize how broad aviation is, in terms of its limits, capabilities, definitions and practices.

 

The max range of an aircraft is one of those discussions that always gets me, and this one is rather similar.  To put it like my land use law professor put just about every answer: it depends.  Max range, much like braking distance, depends on several factors, as some have mentioned.  As such, is it realistic that the PMDG 777 can "stop on a dime?"  Sure, but it depends.  At what weight were you operating?  Was the runway dry?  Did you set down firmly or try to grease it?  These are all factors in how much runway you're going to use.

 

So, is it realistic?

 

Just about as realistic as the difference in stopping distances of a fully loaded freight train versus one just hauling the cars.

 

Remember, we're still dealing with F = m * a here.  There's a reason race groups try to minimize weights in their cars.  For a given force, a decrease in mass equals an increase in acceleration.  Less mass = greater braking potential.  If the 777s brakes can stop the aircraft pretty quickly an a MTOW RTO, think about the braking potential when you're at a lower weight (which you'll always be upon landing...unless you broke physics).

Kyle Rodgers

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