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MED1473

landing distances

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Hi all! Apologies for posting am issues similar to my previous one but since nobody picked that up I thought I'd go for a more general question,so here it is.

when using the landing distance tables on the FCOM which and how do you pick the relevant breaking action?

Regards

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SmartCockpit.com PDF manual, page 4 has the following info:

 

For normal operation of the autobrake system select a deceleration setting.
Settings include:
- MAX: Used when minimum stopping distance is required. Deceleration rate is less than that
produced by full manual braking
- 2 or 3: Should be used for wet or slippery runways or when landing rollout distance is limited
- 1: This setting provides a moderate deceleration suitable for all routine operations
Experience with various runway conditions and the related airplane handling characteristics
provide initial guidance for the level of deceleration to be selected.

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What Ralph said with some small nuggets of practical real world input :)

 

For the Dry, Good, Medium and Poor for surface condition friction, Dry is self explanatory. Good is generally what you can expect from a wet runway. Medium and Poor are generally what to expect from a contaminated runway.

 

In the real world, when conditions may lead to a contaminated runway the ATIS is often suffixed with a runway state code. See the section at the end of this link: http://www.skybrary.aero/index.php/Meteorological_Terminal_Air_Report_%28METAR%29. Check out the Skybrary site in general, it is just manna for the aviation curious!

 

You'll notice that braking actions can be reported as medium/good or medium/poor. Boeing does not supply that data and in reality interpolation is not safe, therefore the correct thing to do would be to go with the worst case scenario. These day airlines generally use EFB performance tools to crunch all the numbers, so it is easy.

 

Now, with regards to brake selection. Autobrake 1 is never used in the real world, especially with carbon brakes as it causes too much wear as this setting the brakes will constantly oscillate between on and off. Autobrake 2 and 3 are used regularly and as for MAX, with 5000hrs on the 73 in the real world I personally have never used it except during sim rides. MAX MANUAL braking is the most braking performance available under any conditions and is assumed for non-normal conditions.

 

You can see that in the FCOM, Performance Inflight, Advisory Information landing distances, choose the Autobrake setting that allows you to comfortable land in the distance available or in good conditions for the preferred taxiway exit (taking into consideration brake cooling schedule for the predicted turnaround duration). When landing on long dry runways with an exit say 3000m in, usually Autobrake is select OFF and just idle reverse thrust coasting in with light manual braking - very civilized.

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I've used MAX several times up in the Arctic on short contaminated runways. Works fine.

 

I heard once of a plane that was given a runway report that called for POOR braking action. The crew selected MAX for the landing. In the meantime, the runway had been plowed and sanded. When they touched down, the MAX stopped the jet so fast, the crew didn't get the engines out of reverse in time and fodded them out.

 

Be careful.

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Using MAX isn't problematic in it self, just the conditions that require it for most operators are so few and far between, is all. Not saying don't use it or it isn't used. For the sake of efficiency and short turnarounds. Levels like MAX are really to assure stopping nicely in the LDA, not to make specific exits.

 

One example where MAX might enter the discussion is a shortish and high airfield. But then brake cooling may also be an issue. This isn't reflected so well in the PMDG tables, but our tables are more limiting - maybe due to carbon brakes or maybe due to updated data. Anyway, such issues are not relevant to NGX, but can be considerations for real planning.

 

 

 


the runway had been plowed and sanded. When they touched down, the MAX stopped the jet so fast, the crew didn't get the engines out of reverse in time and fodded them out.

Jeez! I remember my first time out in the real 737 doing the mandatory circuits, after the touch and goes I landed for a full stop and applied the pedal pressure I got used to in the training sim, BANG! It was like hitting a brick wall, I don't think I even had time to get past the idle reverse detent - lesson learnt :blush:

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I heard once of a plane that was given a runway report that called for POOR braking action. The crew selected MAX for the landing.

 

Do you guys select MAX to leverage possible patches with better action as opposed to patches with braking action unsatisfactory to achieve normal deceleration?

 

Just asking - personally rather than select max I like better to ride it out on manual braking.

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Do you guys select MAX to leverage possible patches with better action as opposed to patches with braking action unsatisfactory to achieve normal deceleration?

 

Just asking - personally rather than select max I like better to ride it out on manual braking.

I think it might be simply to get the brakes up to 3000psi ASAP. I think everyone overrides them pretty quickly, anyway.

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Do you guys select MAX to leverage possible patches with better action as opposed to patches with braking action unsatisfactory to achieve normal deceleration?

If the runway is contaminated (as it must be with a poor braking action) then technically that means that 25% or more of its surface is contaminated, so in reality I suppose patches are possibility. But you would plan according to braking action/friction info supplied.

 

 


I think it might be simply to get the brakes up to 3000psi ASAP. I think everyone overrides them pretty quickly, anyway.

Actually, for landing, the MAX setting confusingly isn't the maximum, it won't use the full 3000psi, only MAX MANUAL will.

 


Just asking - personally rather than select max I like better to ride it out on manual braking

Autobrake MAX is recommended by Boeing when minimum stopping distance is required for landing as opposed to planning on using MAX MANUAL.

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I think it might be simply to get the brakes up to 3000psi ASAP. I think everyone overrides them pretty quickly, anyway.

 

That is a good point, autobrake will be faster than a pilot...

 

 

 


Autobrake MAX is recommended by Boeing when minimum stopping distance is required for landing as opposed to planning on using MAX MANUAL.

 

I wouldn't say that achieving minimum stopping distance in general translates to the same as achieving normal stopping distance on poor surface. But yes - using MAX autobrake and THEN possibly overriding with MAX manual will result in lowest stopping distance.

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I wouldn't say that achieving minimum stopping distance in general translates to the same as achieving normal stopping distance on poor surface.

Landing in a poor surface is one of the sketchiest acts in commercial aviation with the actual stopping distances achieved being very inconsistent with very little hard data available meaning that the term normal distance doesn't really apply! In fact landing on poor surfaces is not permitted by many airlines unless in emergency. If faced with a poor surface landing, the only frame of mind is to landing in the shortest possible distance.

 

If Boeing recommendation is followed, the performance would be calculated for MAX setting. MAX MANUAL could be used once touched down, but as you can see from the performance tables, you can bank on only saving something like 60m or so.

 

So it is all very marginal and all highly dubious unless the airfield in question is a known quantity by the operator!

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Actually, for landing, the MAX setting confusingly isn't the maximum, it won't use the full 3000psi, only MAX MANUAL will.

 

This discussion seems to come up every year in recurrent training. This is my understanding:

 

Manual gives you up to 3000psi based on how hard you push with your feet (it could be less). Max Auto gives you up to 3000psi based on 8.3kts/sec above 80kts and then 7.0kts/sec deceleration.

 

If you aren't getting those deceleration rates, you're getting 3000psi. Again, I override about halfway through the rollout, but the autobrakes can get started before I can.

 

The books don't say you don't get 3000psi, they do say you don't get the same deceleration rates. However, if you're sliding down a runway at 5kts/sec deceleration, manual and Max Auto will be the same.

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Thank you for your very informative answers and the interesting discussion!

Now the question is, how do I apply this to fsx? Using let's say AS2012, are the breaking coefficients actually modelled? Are those tables going to give me realistic data for my simulation and the planning of landing distances?

Thanks

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This discussion seems to come up every year in recurrent training. This is my understanding:

 

Manual gives you up to 3000psi based on how hard you push with your feet (it could be less). Max Auto gives you up to 3000psi based on 8.3kts/sec above 80kts and then 7.0kts/sec deceleration.

 

If you aren't getting those deceleration rates, you're getting 3000psi. Again, I override about halfway through the rollout, but the autobrakes can get started before I can.

 

The books don't say you don't get 3000psi, they do say you don't get the same deceleration rates. However, if you're sliding down a runway at 5kts/sec deceleration, manual and Max Auto will be the same.

 

Yep... but at the same time, when you DO get those values, you don't get 3000psi - on good enough surface. MAX MANUAL - that could then give you 9, 10, 11... kts/sec

 

In the end, using autobrakes becomes important in that they do, in any case, provide braking pressure between the time of their activation and the time that the pilot ceases to be preoccupied with touchdown, keeping track and flying the nose down enough to commence manual braking of his own.

 

All in all I think it's prudent to mention that in poor braking action conditions, it's essential to use other means of stopping, mainly reverse - those are not dependent on runway friction.

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Yep... but at the same time, when you DO get those values, you don't get 3000psi - on good enough surface. MAX MANUAL - that could then give you 9, 10, 11... kts/sec

 

In the end, using autobrakes becomes important in that they do, in any case, provide braking pressure between the time of their activation and the time that the pilot ceases to be preoccupied with touchdown, keeping track and flying the nose down enough to commence manual braking of his own.

 

All in all I think it's prudent to mention that in poor braking action conditions, it's essential to use other means of stopping, mainly reverse - those are not dependent on runway friction.

Yes! I talked to a guy who just had high-speed abort. 120kts or so. He said it was VERY violent with RTO. I don't think I want to experience 3000psi with good braking. I'll be happy with 8.3kts/sec or less. If you need more than that, something is seriously wrong.

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RTO is the strongest braking on the plane. That's when you can get fuse plugs melting

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If you haven't tried the B737NG dispatch sheet for excel can find it at avsim file library: http://library.avsim.net/esearch.php?CatID=fsxutil&DLID=180540

 

It calculates the required landing distance based on speed, brake settings, weather, and runway conditions. It easy to change the factors and see the results.

 

One thing to remember though. The Required Landing Distance is longer that the expected landing role. It includes safety margins. If i remember correctly it adds 300ft to tresshold plus a percentage of the calculated roll distance depending on conditions.

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This discussion seems to come up every year in recurrent training. This is my understanding:

 

Manual gives you up to 3000psi based on how hard you push with your feet (it could be less). Max Auto gives you up to 3000psi based on 8.3kts/sec above 80kts and then 7.0kts/sec deceleration.

Yup, according to my book The Boeing 737 Technical Guide your understanding is correct, thanks for correct me. Another thought is that the maximum normal pressure range of the hydraulic system is 3000 - 3500psi. Where MAX is capped at 3000psi, RTO is uncontrolled and I assume will use all the pressure available to it, which could mean up to 3500 psi on the day with maximum deceleration all the way to standstill. This is the same for MAX MANUAL.

 

 

 

I don't think I want to experience 3000psi with good braking. I'll be happy with 8.3kts/sec or less. If you need more than that, something is seriously wrong.

Have you noticed how the MAX setting is on a latch, you have to pull the control knob out to select it. Perhaps Boeing's way of saying "Seriously - are you sure about this?" :blink:

 

keeping track and flying the nose down enough to commence manual braking of his own.

Nothing dramatic, but I have noticed with Autobrake 3 and specifically landing at a high altitude airfields with a landing ground speed of about 160kts, the deceleration rate is such that the nose has a tendency to drop much very quickly unless slowed with judicious back pressure on the column.

 

 

 

The Required Landing Distance is longer that the expected landing role. It includes safety margins. If i remember correctly it adds 300ft to tresshold plus a percentage of the calculated roll distance depending on conditions.

Landing performance in the Flight Planning Performance Manual (not included with NGX) and the Performance Dispatch (included in FCOM1) is certified and factored data and doesn't assume the use of reverse. The Performance Inflight (FCOM1 and QRH) is unfactored and is what the crews use to calculate landing performance for the actual conditions and assumes the use of reverse thrust (different operators may have not include reverse thrust in their tables). Using this data you can expect the aircraft to stop in the quoted distances. So, if you float the landing you will most likely not meet the numbers.

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