Rwy Contaminated???

[AGODIA]

As an MD-80 operator and curious about the LEGALITY in Taking off on a contaminated rwy. No matter all the bla bla bla in penalties reduction on the weight, I haven´t seen in any of my company manuals that the MD has been certify for this (tested) and I´m not keen to do it with passengers on board.
I still remember Airbus (A-300) warning that thouse figures were a recomendation only, the airplane was not tested for it.
In the mean while a nice cup of coffe waiting for the rwy to be clean sounds good to me.
Any light on this??

[john_tullamarine]

Certainly the manufacturers will have some limited data for severe water contamination ... ie a simple flooded runway situation... as the normal exercise for engine ingestion tests sees the aircraft being run through a big controlled puddle from which some drag data can be obtained in addition to the prime test function.

The real world problem is real world variability... like all this performance stuff... how deep is the water and what is the variation over the runway etc ... in the case of a contaminated situation (slush and snow) the density and depth estimations are a bit finger in the windish.

What one does in the real world situation, then, is fraught with a degree of optimism or pessimism according to one's, and one's company's, views.

My views are coloured by the thoughts that the company ought to prescribe in the OM its requirements and preferences for the guidance of crews. Over and above this, there is always the crew's option to apply the recommended practices in a more conservative manner .... someone has to assess the depth etc of the contaminant ... and ultimately, if considered appropriate, this might include deferring the departure or diverting/holding in the case of an arrival ... presuming, in the latter case, you have the luxury of spare fuel.

I think the main thing is to be reasonably consistent and sensible so you have something to hang your hat on at the enquiry and the chief pilot has something with which to fend off the accountants when they come looking for a hide to pin to the wall after the flight is delayed or cancelled ...

As to legality ... isn't that what the judge decides after everyone has had all the time in the world to review the decision you made in a few seconds or minutes ? ... and you have been made to look a total idiot in the witness box during the said review of the said decision making process ?

[mutt]

AGODIA,

There is no legal requirement for manufacturers to flight test aircraft in contaminated conditions, therefore they don’t!

They normally present data titled “For Information Only” which is based on parameters established by NASA in the 1960’s using a Convair 880. The FAA has tried to regulate Contaminated runway operations. Their latest missive is AC91-6A but as the name suggests this document is over 10 years old, during which time the aviation industry has failed to consolidate the information into the FARS, but you are expected to use this information to make a correct decision every time you takeoff…………

Unfortunately if something goes wrong it will be you sitting in the court of law and not the airline industry for failing you…..

Good Luck.

Mutt.

[Shore Guy]

The data certainly exists for computations on contaminated runways - however there is no regulatory requirement to apply any of that data for takeoff. Just imagine the runway requirements for a high speed abort on a contaminated runway in a large transport aircraft....you would need the Bonneville Salt Flats to stop it (remember, no reverser for performance computations).

The ATA and FAA I think are in bed on this topic. It always has amazed me that certain really non-consequential performance calculations are required and carried out to the third decimal point while this GIANT loophole exists.

[john_tullamarine]

Shore Guy,

Much in the way of estimates is available ... not very much in the way of hard data (as in experimentally verified numbers)

In this neck of the woods, the rules HAVE, for as long as I can remember, required the operator to apply a suitable correction for runway degradation .. they have, however, never got down to the nitty gritty of how that sort of thing ought to be done .... so some of the operators ... sort of ..... hope that the problem either won't bite them or will somehow go away ...

Perversely ... the ASDR becomes less of a problem as the contamination increases due to increased drag associated with the aircraft's having to play motorboats ... as you would understand, being a boatie .... the continued takeoff consideration is, on the other hand, a major worry.

Nothing at all inconsequential about either the calculations or the physical significance of the problem ...

Mutt has more detail on this stuff than I do ... perhaps he might put his cap and gown on and produce a comment or three for the interest of all ?

[Shore Guy]

All,

The only performance degradations for takeoff calculations that I can recall dealing with contaminated runway operations on FAR part 25 aircraft are the various clutter charts (U.S). However, landing data reflects wet/dry with (variable) recommendations (non-regulatory) for MU and/or runway condition reports. A high speed abort on takeoff is (1) at higher weight and therefore (2) higher speed than landing for a given trip, however there is no regulatory requirement to have runway friction information incorporated in takeoff computations to guarantee the safety of a high speed reject.

I do not believe that this is an oversight or coincidence. To quantify this data and apply it in a regulatory fashion would shut down most takeoffs on a contaminated runway.

[Shore Guy]

Let me add the "Reduced V1" charts for most aircraft (contaminated runway takeoff).

[mutt]

Shore Guy,

The “clutter charts” that you are talking about are based on a specific runway friction derived from the aforementioned NASA testing.

Although we are not legally obliged to use this data, surely we are morally obliged to?

Mutt

[lomapaseo]

The MD80 has had two near accidents after operating on contaminated taxiways.

The problem stems from slush ridges from recent snowstorms where the runway is reasonably clear but the taxiways have ploughed ridges to taxi through.

After the aircraft becomes airborne the pilot diiscovered difficulty in raisng the gear, After a couple of cycles the gear stowed and so did the engines as they both ingested 20 to 30 pounds of iced slushed jamming the gear.

[Shore Guy]

Mutt and all,

I am under the impression that clutter charts and clutter correction not so much relates to runway friction as it does for the aircrafts acceleration characteristics with the "restriction" of clutter -standing water, slush, non-compacted/wet snow, etc.

For example, an aircraft would actually accelerate (slightly) faster on a runway with a very low co-efficient of friction with no clutter (glare ice). V1 would be reached sooner in time and position on the runway. Stopping in this situation would be another matter altogether. Clutter relates to the restriction of the aircraft to accelerate to takeoff speeds. Although a cluttered runway implies reduction in coefficient of friction, the clutter itself would actually help the aircraft decelerate in the case of rejected takeoff.

[AGODIA]

Just came back from a flight and like to thank to all the folks in the forum about my question.
I agree with you that all the figures should come out to blame any one of us in the worst situation....it´s always been the same...
I still will hold on that cup of coffe in a real situation, and doing all the funny calculations at the winter operations simulator...
and get the coffe break later

[Semaphore Sam]

Hi Mutt! The charts we use in the 747-400 have certain very strange characteristics. For example, in certain circumstances, as you increase the depth of contaminant, allowable takeoff weight increases. This leads to the theoritical case where the flight would have to be delayed til more snow covered the runway. I bring this up during recurrent each year; everybody scratches heads, then we proceed to the next subject.

Do I trust these charts? Right up front the FAA says they are not 'certified' for use. There is only one right answer...wait for the plows!

[mutt]

Semaphore_Sam,

If you think that the 400 is strange just wait until you move to the pocket rocket. :)

I am extremely disappointed that no one has explained this to you in recurrent :(, In JT’s comments above he compares an aircraft to a boat, this is rather simplistic but true, as the depth of contaminant increases it reduces the aircrafts acceleration but greatly aids the aircraft’s ability to stop.

The following are an approximation of the acceleration rates.

Dry - All engine acceleration = 3.5 kts/sec
Dry – One Engine Inop acceleration = 2.3 kts/sec
6 mm – One Engine Inop acceleration = 2.0 kts/sec
13 mm – One Engine Inop acceleration = 1.5 kts/sec

From this you can easily see that 13 mm of contamination is worse than 6mm, but then we have to look at stopping….

Dry – One Engine Inop deceleration = 8.0 kts/sec
6 mm – One Engine Inop deceleration = 3.0 kts/sec
13 mm – One Engine Inop deceleration = 3.5 kts/sec

Your takeoff weight is a trade off between the accelerate go and the accelerate stop, with the greater stopping ability associated with 13mm you will usually see better weights!

As for the FAA certification, I’m at a loss as to how they have avoided this subject for so long. I guess that it just doesn’t snow in North America.

Cheers.

Mutt.

[john_tullamarine]

... and I usually get caned for not being simple .... must be a happy medium somewheres ....

[Semaphore Sam]

Hi John! (M)
I take your point...better 26 mm contaminant than 4mm, due to increased braking. Why is the limit at 13mm? Why not 8 feet,when braking action is sooo much better?

Potential Captain's announcement: "Sorry for the delay; we have inadequate runway contaminant; if it snows another 8 mm, we'll be ok for takeoff; til then, we must endure further delay."

I still say: "Wait for the plows; no plows, no go!" If the the FAA stands by the figures. ok. Until then, I understand the meaning of 'Information Only', only too well. It means, "If I trust the figures provided, and have an 'incident', I've just provided x number of lawyers with a steady income for x months, as well as destroying my career." Truly a fool's choice.

SS

[john_tullamarine]

.. because the probability of successfully continuing with an OEI takeoff becomes depressingly remote ....