Landing distances

[Olendirk]

Hey guys,

what is the difference between landing field distance required in flight and in preplanning? What is the distance i get from QRH? And when are the safety factors applied of 1.67 or for wet 1.92?

Thanks!

OD

[Old Smokey]

Olendirk,

At the Pre-Flight phase, you must ensure that the Landing Distance Available (LDA) is equal to or greater than the Demonstrated Landing Distance, factored by 1.67 for DRY runways, or 1.92 (1.67 X 1.15) for WET runways.

If you dispatch with a known MEL affecting landing distance, then the extra factor (or distance) for the deviation must also be factored. For example, Anti-Skid Inop may specify that the Landing Distance Required for a dry runway is 1.3 times that for normal. In this case, the LDA must equal or exceed LDR X 1.3 X 1.67, i.e. LDR X 2.17 at the time of departure. If however, the aircraft departed with no abnormalities, but Anti-Skid became inoperative in flight, you may then use the 0.67 'buffer' provided for at the time of departure. Put another way, you dispatched with 0.67 X LDR available as a buffer, and you may now use some of it, i.e. 0.3 X LDR to accomodate the deficiency.

Regards,

Old Smokey

[Olendirk]

Sir!

thanks a lot, but in flight? What distances do i get from the QRH?Do I have to factor them?

Thanks!

OD

[Ex Douglas Driver]

I should say somewhere on the chart whether it is factored or not.

[Old Smokey]

Olendirk,

AOM and QRH's will vary, some will provide the factored landing distance, and some will not. It's up to you to check this, it should be clearly indicated in the content of the AOM/QRH.

What is important in the in-flight phase, is that if a new abnormality indicates a factor or additive over the NORMAL landing distance, then you should apply the correction to the normal landing distance to find the 'new' landing distance. This is then compared to the LDA. In-flight, you do not have to apply the 1.67 or 1.92 multiple, this should have been considered pre-flight.

An example - You depart with no abnormal configuration, and for your planned landing weight and environmental conditions the Landing Distance is 1000 M for a dry runway. You must ensure that the LDA at your destination is at least 1670 M. Let's assume that the LDA is exactly 1670 M, so you depart with just enough LDA available for arrival. En-route, Anti-Skid becomes Inop, and your QRH indicates that the landing distance required is 1.3 times that of normal, i.e. you now require 1300 M. As you have 1670 M available, you may continue and land, there is no need to add any further factor to the new 1300 M landing distance required.

Regards,

Old Smokey

[john_tullamarine]

However, consider the arguments at the Enquiry.

In flight ..

(a) if you have but one diversion option, then you do what you have to do

(b) if you have multiple diversion options, it would be useful to have considered the use of runways with all or part of the certification factors ... bit embarrassing if you slide off the end of the diversion runway and another, longer runway would have been more or less equally a solution to the problems at the time of the decision ... ?

All a case of considering all the information as part of the decision making process ....

[guclu]

The Actual Landing Distance as you know is calculated with a lot of factors standardised. To mention some of these .

- The a/c is at 50ft above runway threshold
- the approach speed is at Vr + 5
- the pilot applies max braking
- antiskid is operating
- the ground spoilers are operating
- thrust reversers are not taken into account

and some unclear factors as:
- the wear of the tires
- the wear of the braking system
- actual runway surface friction

So no big deal to understand that the actual landing distance is your final point when considering a suitable runway.

When in flight you experience an emergency (which means you have to land at nearest suitable airport) you have to check the actual landing distance and need not factor it with the above values. But if you are going to land at the exact value you shouldn't forget the above assumptions.

The point is you have little room to play when you are planning to land to a runway that is exactly or close to your actual landing distance reqired.

Hence, for normal operations you are factoring the actual landing distance required with the above values to cover for factors like,

- slight airspeed variations
- slight tail winds
- long flare
- normal braking (passanger comfort and money)
- not new tires
- etc.

Hope it helped.

Guclu

[oldebloke]

AS all the guys have said for Dispatch one needs the 1.67(dry)or if the wx at dest is below 300'/wet one needs the 1.92.
Nowadays once airbourne,should a systems failure develop check the ACTUAL landing distance in the QRH/AFM/FCOM ,and factor this distance as advised by the increment required for the failure(loss of braking systems/hydraulics.etc require 2.1 total distance)..if not always ask for the longest runway or divert to a good into wind runway..:ok:

[Old Smokey]

In the last few posts there's been some good discussion in considering diversion to a more suitable airport. The consideration of a diversion to a more suitable airport forms a part of the decision making process in countless 'non-normal' circumstances, rangeing from better medical facilities for a sick passenger, to better RFF facilities when they might be needed, or, in line with this topic, longer (or more into wind) runways are available.

I think that the best point of all was brought up by guclu, who has indicated to us the means used by the test / certification pilot in establishing the Landing Distances required. The test / certification pilot uses somewhat aggressive techniques which are rarely used in day to day line operations, e.g. crossing the threshold at 50 feet and closing the Power/Thrust levers completely at that point, landing on the 300 M / 1000 ft touchdown point, through to the use of Maximum braking. We don't do this on every-day operations.

If an alternate airport / runway offering normal margins of Landing Distance is unavailable, and the pilot is then committed to landing on a runway with adequate, but less than the normal length margins available, I believe that he/she should bear in mind the means by which the demonstrated landing distances have been achieved, and operate accordingly.

That is - Close the Power / Thrust levers at the threshold, aggressively (if necessary) 'put' the aircraft on the touchdown markers, apply MAXIMUM braking, and use FULL reverse, all the way to a stop if necessary. The Reverse Thrust is a bonus, and will hopefully accomodate for any small deviations from non-perfect speed control, slight wind variations, etc. Bear in mind too, that, at the pre-flight planning stage, no credit can be taken for the Landing wind component, and any Headwind component upon arrival will also be a bonus.

In this case, passenger safety is the primary consideration, passenger comfort is an unaffordable luxury.

Regards,

Old Smokey

[cdb]

As an ATCO, could you clarify:

Aggressively (if necessary) 'put' the aircraft on the touchdown markers,

Well, assuming you were visual at a couple of miles, why wait that long? Whats to stop closing the throttles earlier and "Putting" the aircraft on tarmac at the threshold? That would give you an extra 1/3 of runway to play with.

I realise it might make a go-around more difficult because of spool-up time, but even on a normal landing wheels hit the deck from a go-around at the threshold don't they?

[Old Smokey]

I should have said "assertively", not "aggresively". A bit of overkill, sorry.

Regards,

Old Smokey