Landing performance / Data and Calculations

[Driver 170]

Some of you may know i'm in no way a pilot but i do however, have a set of SOPs from a UK and Europe operator.

I was reading through there line training Doc and QRH - it mentions, distance and adjustments for, GOOD, MEDIUM and POOR are increased by 15% but it also mentions in the advisory information part of the QRH Normal conditions - 115% for Slippery runways.

I understand the wet figures are the dry factored figures increased by a further 15% but what is the 115% for?

[Intruder]

Simply a safety factor. Dunno how they came up with the number...

[Driver 170]

So that 115% is added to the runway length if its CLD cntm ?

[Driver 170]

Do they pilots work all this out at the planning stage (preflight) do they have to work out to make sure the landing mass of there aeroplane is stopped within 60% of the LDA ?

[Driver 170]

It says in my DOC;

The dry figures in the QRH are the actual landing distance i.e. unfactored while GOOD, MEDIUM etc. are factored by 1.15 (15%).

I thought 1.15 is 115% decimal of 115 is 1.15 ???

[Wirbelsturm]

In our older landing performance manuals we used to be given the data supplied directly from the aircraft manufacturer and obtained using test pilots in controlled conditions!

As most of us know (and occasionally a few don't) we are not test pilots so the data was factored for safety to allow for slight float, slightly varying speeds and generally a slower application of braking.

Our new manuals have the safety factor included in the given distances for normal operations hence making it unnecessary to apply safety factor corrections as they are already there.

In non-normal conditions where you might have a technical malfunction then the data is exact as per the test pilot version and you have to add the safety margins yourself. This is there because you might need to know the best possible braking distance for your current config in the event of an emergency. Then add on your safety margins to see if the approach and landing is viable.

Slippery runways would normally come under contaminated runways but not always and the performance manual states:

Slippery Runway landing data published in the Performance manual is the actual demonstrated data PLUS a factor of 1.15 (15%) added for JAR certification requirements, and the runway is NOT contaminated, which BOEING have chosen to equate to a runway covered in wet ice.

So the 1.15 comes from a JAR (EASA) requirement to add an extra 15% distance on to the distance already calculated for landing on a slippery runway. Contaminated figures already meet the factored certification requirements. Flooded runways for example are always to be considered 'slippery'.

Hope that helps.

[Driver 170]

So, on my Performance Reference Handbook it mentions - Certified Landing Distance on a Contaminated (Slippery) runway (CLDcntm) is the longest of CLDwet and 115% of the required landing distance in accordance with approved contaminated runway landing distance data.

Does this mean that CLDdry has got an extra 15% or 1.15 margin added ??

[Wirbelsturm]

You should have a reported runway state which will tell you the level of contamination of the runway and the associated braking action for that contaminant.

Icao codes run:
6-dry
5-wet, frost, water or slush upto 3mm deep
4-Compacted snow <-13C
3-wet (slippery),dry or wet snow upto 3mm, compacted snow <-3C >-13C
2-Water or slush > 3mm, dry or wet snow >3mm, compacted snow >-3C
1-Ice
0-Water over compacted snow,Dry or wet snow over Ice/wet ice,Ice >-3C

This will give you your braking action which is then applied to your landing performance.

ALD is the actual landing distance required to bring the aircraft to a stop from 50' above the runway.
A safety margin is applied to the ALD in accordance with EASA Ops
Required landing distance RLD is as follows:
RLD (dry) = 1.67 x ALD on a dry runway
RLD (wet) =1.15 x RLD (dry)
(effectively 1.92 x ALD)

RLD(contaminated) = 1.15 x ALD on the contaminant specified as the table (0-6) above.

So you would ascertain the contaminant, calculate the braking action dependent upon the contaminant (dry, good, good-medium, medium, medium-poor, poor, nil), enter the landing performance tables for the given weights, braking actions and met then multiply the distance given by 1.15 or 15%.

So, for the Boeing 777, the reference distance on a DRY braking action runway is 1185m at max manual braking, the same distance with POOR braking distance is 2555m so taking into account no other factors if the runway is contaminated I would need 2555m * 1.15 which would be 2938m

[Driver 170]

You just nailed it on the head thankyou! I will keep on reading :) i'm finding all this quite interesting.

How do you best judge distance to your desired runway exit? My SOPs mention brake to vacate. Do you use the measured NM strip on the charts and compare that to the runway exit from the threshold? As we know 305m of air distance is factored in from 50ft above the threshold.

[Driver 170]

Just noticed you mentioned

Enter the landing performance tables for the given weights, braking actions and met then multiply the distance given by 1.15 or 15%.

But isn't that 15% already added to the GOOD, MEDIUM and POOR, PI QRH data?

[Driver 170]

So if the runway is WET or CONTAMINATED you add 115% to the ALD?

[Wirbelsturm]

But isn't that 15% already added to the GOOD, MEDIUM and POOR, PI QRH data?

You are quite correct, my mistake. It states, for 'normal operations' that:

'All reference distances and adjustments show have been increased by 15%'

Contamination may well degrade the braking action further due to aquaplaning, slush or snow build up under the tires etc. Therefore the tables will give you ALD then factor 15% for safety.

At the end of the day it is a judgement call as no amount of tables could cover the infinite number of variables that mother nature throws at us.

As for choosing exits it is just as you say, look at the landing distance to the exit you want and then calculate what configuration is going to give it to you 'comfortably'.

[Driver 170]

I suppose its alot down to experience too! Something i won't gain.

[Denti]

And then there is that pesky distinction between dispatch landing performance calculation and inflight landing calculation which is based on raw AFM data (unfactored) plus a much lower general factor, like 15 or 20%.