A320 QRH In Flight Performance landing distance
 

With respect to the A320 QRH - In Flight Performance landing distance ( both without and with failures) is anyone really aware whether these figures include an additional safety margin or are they actual figures?
I did hear a strong opinion in the past that these are actual figures but after some search I could not locate anywhere officially such assertion.

The QRH landing distance is defined as

Your airline should deem if there’s any extra factor (we are recommended to add an extra 15%). The LD above will be more than the Actual Landing Distance which is used to work out the Required Landing Distance at dispatch (e.g. RLD dry =ALD/0.6)

From the QRH, the figures does not include the safety margin (15%). The 15% margin becomes too restrictive during emergency. So depends on situation and airline policy.

Attached are the slides given during Airbus rep presentation.

This is not from ALD, historically the pilots would start with an actual landing distance and then factor this with a factor depending on the failure. Now days post roughly 2012, the in flight landing distance is already made more realistic (more factors built into the calculation in accordance with the TALPA/ARC model). This is to make it more realistic of a line pilot. But as far as flight crew are concerned the result of an in flight landing distance is not factored! Therefore according to airline policy an additional factor is added. Airbus recommend 15% but this can be removed in the case of exceptional circumstances.

Check the annotation on the paperwork.
Airbus basic publications appear to be Operational Landing Distances, OLD (unfactored); however by customer choice, or for all FAA operators the minimum 15% factor is included, Factored OLD = FOLD.
Electronic formats may also have the choice between OLD and FOLD, and a selection to increase the factor.

http://www.airbus.com/content/dam/co...agazine_12.pdf Pages 5 - 8

Has anyone every noted how inaccurate these figures are using either the simulator or real life? The amount of factors being factored in have, IMHO, made the figures ridiculously conservative.

This is compounded by the fact that in the sim in practically every non normal scenario reverse is reduced to idle by 70 knots and manual braking inevitably comes in and the aircraft is allowed to roll on a bit once the aircrew realise they have in fact, 1,000s of metres of runway left to stop in.

Forget the fact that 90% of Airbus pilots aren't aware of the logic of Autobrake Medium and how it affects us on a practical basis.

We seemed to have moved from accuracy to avoidance of liability.

Maui, first, the changes in calculating landing performance were driven by the need to address one, of not the most serious safety risk in operations.

I did seen a comparison of the new performance base - OLD, against the certificated (AFM) performance - more searching to do (Boeing / Airbus, TALPA meeting?). The performance data were remarkably close which suggest that the industry, those operators not using the full landing factors, have been exposed to significant risk, which in some circumstances have been borne out by accident figures.

Second, the simulator is a model - it is a representation of an aircraft and not reality. A manufacturer may only have dry landing performance for comparison because this is the only requirement for certification, yet that data probably does not account for differing runway surfaces or brake wear ... and particularly piloting operation and perception.
There is similar variability with aircraft and actual operation, but there should not be such a great difference on a dry runway. However on wet runways and particularly contaminated runways there probably is much wider variation.
Always consider how representative a landing may be vs the method of calculating landing performance - speed, wind, TCH, float, spoilers / reverse timing, brake/tyre wear, runway surface, ...

Nothing is ‘accurate’ in aviation, just an approximation which pilots have to manage. Having a bit more margin to help manage the unexpected reflects an attitude to safety, which if maintained negates the need for liability.

# 6 [ Exactly what are 90% of Airbus pilots not aware off? ]

Our flysmart landing distance is pretty accurate. If, for example, you are using autobrake low, land in the right place and leave it in until you stop you will end up somewhere between the LD and factored LD (+15%) from the threshold.

Maui, I would appreciate being enlightened with your autobrake knowledge, too. Please share it - sounds like the kind of thing that could be useful when faced with a smart arsed sim instructor!

Yes, what logic are you referring to, and which type? 330? 321? Slightly different animals. 330 timing of brake application is different depending on the setting, which can affect technique for reverse and derotation. Can't think of any other real gotchas though. Have actually seen higher brake temps using LOW in certain wind and weight conditions when reverse JUST ABOUT achieves the required deceleration rate, causing the brakes to cycle on and off (which carbon brakes absolutely LOVE).... doesn't happen at MED even with max reverse.

And yes A/BRK medium in the 330 at PHOG with a 25 knot headwind does get you stopped in a hurry. Just release the back-stick a little and let the second set of wheels roll on before the brakes kick in and it won't feel so extreme. Some people say going straight to max reverse ASAP reduces the "slam down" a little (as opposed to going to idle reverse for a moment first to let things spool up evenly). Personally that didn't work for me; I found that just learning the timing of the brake application and doing whatever is necessary with the sidestick to keep the derotation rate visually the same as with LOW brakes, did the trick.

About 50% of the time. The rest is witchcraft.

Apologies; I've been away. And I'm sure most heads will be aware of it on here, I just find in conversation with a lot of pilots they are unaware of the logic behind autobrake Med on the A320 family...

MED has two phases:
Phase 1) Limited declaration is progressively applied without delay until the attitude is less than 1 degree or T= 5 seconds. The limit initially is 2m/s here.
Phase 2) Once attitude is less than 1 degree or T = 5 seconds; full MED decel is progressively applied - 3m/s.

Now I notice it on the line when people are keen to make an exit but also make efforts to overly gently lower the nose and there is a distinct two phase decel and we sail past the exit after all the careful calculations are done. 5 seconds at 140 knots being 'progressively decelerated to only .3m/s above autobrale LO eats up a lot of runway.

After discussion, I find, pilots are unaware of the above logic. This is because in our FCOM and previous airline FCOM it is not mentioned. The above numbers are found in the AMM. There is a nice graphical representation in my one at AMM Figure 32-42-00-31600-00-A / Sheet 1 Auto Brake Control Modes.

I hope that illuminates the area and I would be interested if other operators provide that info in their FCOM available to crew.

Very interesting; not in the FCOM but makes sense thinking about how the deceleration feels. Will have a look at the maintenance manual and look that up. Thank you for the reference!

It's not in my FCOM either but I think I've felt something as described by Maui...

I started digging after regularly feeling that two stage deceleration and wondering what it was all about. Digging into the AMM I discovered this info. I actually think it's very valuable information and as per the usual KISS principle the figures are designed to reflect the average line pilot. In this case, you would have to assume the two stage ramp up deceleration and I believe the QRH/EFB already factors this in. Ergo you can beat the figures using the correct technique on a dry runway and autobrake MED, idle reverse.

A real world example of this is CPH 22L. From the threshold to the intersection is about 1,100 meters. I would often ask PM if they think we can turn right onto the intersection to vacate and they would say no chance. And it is in fact, easily achievable. However the EFB would give numbers around the 1,600 meter mark. That's almost a 50% increase! Never mind a 15% margin! This example uses idle reverse also and at nominal weights, nil wind or less than 10 knot headwind. Also taking the corner at 15 knots too.

ATC always seemed slightly surprised when we asked to take 30 to vacate...