Contaminated Runways & autoland

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Why is it that on a contaminated Runway a take off with Derate is allowed but Assumed temperature is not?

Also why isn't autoland allowed on a contaminated runway?

Thanks is advance
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[ACMS]

No autoland on a contaminated runway?

mmm I'll have to look that one up, never heard that before on the 777.

[FlightDetent]

Airbus wording (A32S): Automatic rollout performance has been approved on dry and wet runways, but performance on snow-covered or icy runways has not been demostrated.

[A330AV8R]

max you can do on a contaminated rwy is CAT IIIA not B as the latter requires autoroll out speaking about the A332 series and if I remember right it was the same case on the A320's as well as the 40's

[411A]

Certainly depends on the aircraft type and the specific operator.
Example.
With some L1011 operators (but certainly not all, in the past) autolands to CATIII standard were fully approved on contaminated runways (wet, but not icy, snow OK) with crosswind limitations (15 knots), and full rollout guideance was always available.
Derated and flex takeoffs were also permitted on wet runways, provided anti-skid was fully functional.

[Bredrin]

If you read the difference between derate and flex/assumed temp take off, you will know why derate is allowed but not flex. Just dont go full power at V1 using derate or you may end up off the side of the runway.

[ACMS]

Well if you are above VMCG then going to full power at V1 should be ok shouldn't it?. Might be better than running off the end if the thing's not performing as well as expected.

I just went through 10 auto takeoff data cards on our 77W's to confirm that:-

Only T/O rating and weight effect the VMCG.
Flap setting and temp have no effect.
Contamination has no effect on VMCG.

The biggest difference between VMCG for TO2 and TO is 13 kts.

On the 77W the highest VMCG is about 124 and the lowest V1 you could ever see would be about 122. ( 200 tonnes, TO2 and wet ice )

So for the 77W you can nearly always increase thrust to max at V1 and know you are above VMCG.


Now this is for the 77W, I don't know how other types go?

Anyone?

[john_tullamarine]

.. couple of thoughts ...

if you are above VMCG then going to full power at V1 should be ok

maybe yes, maybe no. First point is that you won't know what your margin on the "real", as opposed to certification, Vmcg might be. Second is that you add some dynamics in the engine thrust run up .. which might bite you on the tail. I did the site investigation on one fatal where just this consideration was the most likely circumstance for a Vmca departure just after lift off. If you are intending to run up the thrust .. do it slowly. Obviously the concern reduces as the margin above Vmcg increases ..

Contamination has no effect on VMCG.

Given that the problem is one of directional control and that any crosswind is going to affect both the turning moments and tendency to slide laterally .. I would be VERY interested in the extent and effect of contamination in general. Caveat - I have no information on the technical basis for whatever your manuals for the aircraft say specifically. On another tack .. why erode your limit margins if you don't have to do so ?

[safetypee]

Q “Why is it that on a contaminated Runway a take off with Derate is allowed but Assumed temperature is not?”

Derate is a limit power setting, which in the context of the question would be maximum thrust.
Assumed temperature calculates reduced thrust settings, which are not authorised – CS 25 Large Aircraft Amendment 5 (http://www.easa.eu.int/ws_prod/g/rg_certspecs.php) AMC 25-13 Reduced And Derated Take-Off Thrust (Power) Procedures (page 739),
“f. (1) Are not authorised on runways contaminated with standing water, snow, slush, or ice, and are not authorised on wet runways unless suitable performance accountability is made for the increased stopping distance on the wet surface.”

Also, see:
Difference between derate and flex. (www.pprune.org/flight-testing/190430-b737-b727-afm-limitation-thrust-increase-engine-failure.html#post2100936)
AIC 86/07. (www.nats-uk.ead-it.com/aip/current/aic/pink/EG_Circ_2007_P_086_en.pdf) “4.1. (f) maximum take off power should be used.”
AMC 25.1583(k) Maximum Depth of Runway Contaminants for Take-off Operations (p 664).

Q “why isn't autoland allowed on a contaminated runway?”
Autoland performance usually has a specific landing performance section - “The landing distance required must be established and scheduled in the aeroplane Flight Manual if it exceeds the distance scheduled for manual landing.“ (JAR-AWO 142).

CS 25 AMC 25.1591 (p 665), provides the basis for landing performance on contaminated runways. There are assumptions about flare distance/time which may not be achievable with an autoland system, thus specific calculations / tests would have to be conducted to establish the performance. It could be argued that this should also apply to HUD landings and non HUD manual landings when using a long body 3 bar VASI.
Contaminated landing performance can claim credit for reverse thrust (differing from wet), if so then this might require demonstration (proof) of a higher reliability for obtaining reverse during an autoland (the Midway landing accident report might refute wisdom of considering this).

Info:
AIC 86/07. (www.nats-uk.ead-it.com/aip/current/aic/pink/EG_Circ_2007_P_086_en.pdf)
1.1 Operations from contaminated runways, by all classes of aeroplane, should be avoided whenever possible.

2 6 It is difficult to measure, or predict, the actual coefficient of friction or value of displacement and impingement drag associated with a contaminated runway. Therefore, it follows that aeroplane performance relative to a particular contaminated runway cannot be scheduled with a high degree of accuracy and hence any 'contaminated runway' data contained in the Flight Manual should be regarded as the best data available.

8.3. … A landing should only be attempted in these conditions (wet contaminated) if there is an adequate distance margin over and above the normal Landing Distance Required and when the crosswind component is small. The effect of aquaplaning on the landing roll is comparable with that of landing on an icy surface.

Autoland on Contaminated Runways. (www.pilotosdeiberia.com/areatec/airbus_sfo/21autoland_contam.htm)

[ACMS]

Hi john, well I did say "should be ok" And I didn't say "slam it to full power either"

If for what ever reason you find yourself getting short of the black stuff ( although it may be white !! ) I think it's better to add a bit of power if you are above the VMCG for that power setting than to run out of runway. Although one would hope that you recognised this problem a bit earlier and stopped.!!

I was trying to point out that on the 77W atleast 99% of the time you will be above the highest VMCG. The exception being very light weights ( 200 tonnes, which is empty ), To2 rating ( 20% derate ) and a contaminated runway causing a low V1

If you know your aircraft then this shouldn't cause too much headache.