Long landing roll (pax question)

[Evening Star]

Something that intrigued me a few weeks ago. Landing at DME with an air temperature of about -10, extensive snow cover and an apparently icy runway. Landing and slowing down was, understandably, very gentle. However, what interested me was that unlike the normal landings at DME I was not aware of much use (if any) of the thrust reversers, and only minimal use of spoilers. Forgive an interested pax asking what may be a dumb question, but I presume this was due to the particular conditions. What are the braking arrangments for a landing like this? I am presuming it is rather like driving on ice, which is basically do nothing sudden, so to stop it is sometimes just best to drift gently to a halt without much use of brake.

Another aspect of that landing was during the taxi there was, for a while, a noticeable smoke haze in the cabin, sufficient to cause comment amongst some of the passengers. Explained to Mrs ES (who is a very nervous flyer at the best of times) that the haze was residual oil from the APU, which seemed the most logical non-dramatic explanation. Was I right?

[Mr Levitator]

The Haze was almost certainly caused by the cabin being depressurised after landing (from around -200ft landing elev). If there was any oil in there it would have really stank!!

Are you sure that the crew didnt just select idle reverse? This is quite common and it doesnt make hardly any noise. I am not sure where DME is???? but if it has a whopping long runway, this is prob the reason to select a slow rate of retard. Usually even with a massive runway, most operators want to get the aircraft stopped and on stand as quickly as possible, with as short a taxi as possible and longest brake cooling period. So when the braking action is good, I'd imagine this is what the crews will go for-when the braking action is poor, I certainly would do what this crew has done and take it very easy stopping the aircraft with a big runway.

Hope that helps

Mr L.

[expedite_climb]

DME = Moscow. For a second there i was thinking distance measuring equipment...... doh !

[BOAC]

ES - the other cause for 'haze' in the cabin COULD be ingestion of runway de-icing fluid via the engines (in reverse) and into the aircon system. Some operators require air con 'OFF' for landing on 'contaminated' runways and it is worth bearing in mind WHAT has been used to clear the runway.

[Spitoon]

A few years back there were a number of incidents, some involving evacuation on the runway, when urea prills were ingested into the engine as reverse thrust was applied.

The aircraft that seemed to be affected were the then relatively new B733/734s. Inside the aircraft I believe there was a light misty smoke with an acrid smell when it happened.

Not a problem these days, certainly in the UK, because prills are no longer used for environmental reasons.

Just in case anyone hasn't come across urea prills, they were pellets of urea that absorbed moisture on the runway surface and then mixed with the water to lower the freezing point. If you didn't get them down early enough they just sat on the icy surface and blew away or got ingested in low slung engines. :uhoh:

[EFP058]

However, what interested me was that unlike the normal landings at DME I was not aware of much use (if any) of the thrust reversers, and only minimal use of spoilers
It is a common misconception among the non-flying public that spoilers are being put up after touchdown to aid the aircraft in slowing down by increasing the aerodynamic drag.

However, the additional drag by spoilers is rather negligible. The job of the spoilers is actually to disrupt the airflow over the wing and flaps, thereby destroying their lift. That in turn makes the aircraft put its entire weight on the wheels, which a) helps in maintaining directional control and b) makes the wheelbrakes much more effective.

There is a difference between flight spoilers (airbrakes) and ground spoilers (lift dumpers). They both use the same panels on the wing, but the flight spoilers usually uses only half or so of them, and also their rate of erection (I hope this doesn´t sound bad in english, because it sure does in german... ;)) is less than that of the groundspoilers. For you do want to disrupt the airflow somewhat (which is what slows you down... not the increased drag of the panels facing the wind), but not destroy the lift altogether. That might be rather unpleasant inflight. ;)

Also, airbrakes work better the faster you are. When you are slow they lose most of their effectiveness. Of course there are a lot of machines where the airbrakes are not effective to begin with, no matter what envelope of the flight you are in. The 737NG family springs to mind, where it seems the airbrakes´ only use is to make noise and shake the aircraft. ;)

[Evening Star]

Thank you all for your replies. Sat back at my window seat I really love to know everything that is going on.

The haze had a definate 'organic' smell to it, so it seemed immediately obvious that it was not just associated with depressurisation. (As an aside, the effect Mr Levitator describes I did see, quite impressively in fact, during the summer on one of Siberia's TU154's.) 'Organic' could indeed cover urea and knowing what I know about Russia (wearing my environmental scientist hat here) if it works they would use it and not bother about the environmental consequences. Furthermore, the aircraft was an Airbus 319, so lowish slung engine a la 737.

EFP058, I am happy to say I did already know about the purpose of spoilers, although rereading my initial post I can understand why it is possible to assume I was falling into a misconception. However, what you write does help clarifying my understanding and I thank you. It would be better if I wrote that in this case we had a very smooth, almost imperceptable, touch down followed by minimal use of spoilers. As I understand it, with icy runway conditions making firm contact is risking trouble, so the minimal use of spoilers will allow some residual lift followed by using the full runway length to allow speed and residual lift to decay with only minimal use of active intervention (reverser/brakes). Am I on the right track?

rate of erection (I hope this doesn´t sound bad in english, because it sure does in german...

Worthy of Jet Blast ;) :ok:

[EFP058]

Evening Star,

I had a feeling this erection thing would not be the best way to say it, but with english being only my third (or fourth) language, I am excused... :p ;) What I was trying to say is: When selecting spoilers in the air, the most they will go up is usually around 30 degrees or so, while on the ground they go up all the way (usually around 60 degrees on most aircraft), plus the number of panels going up is bigger when on the ground.

As for your assumption of selecting only very little groundspoilers: Rather unlikely. The way it (usually) works is, you move the spoiler handle into the "arm" position during approach, and once you touch down and the aircraft registers WoW (Weight on Wheels), the spoilers are being raised all the way automatically. There is no way for you, the pilot, to arm it to open only halfway. It´s either all or nothing, no in betweens.

Although I´m sure someone will prove me wrong in a minute by saying there is some sort of obscure aircraft out there that actually does offer that option. ;)

[Seat1APlease]

I don't know about DME, in my day we used SVO, but could airfield layout also have a bearing?

Airports tend to concentrate snow and ice clearance on the runways rather than the taxyways and aprons which can build up a lot of packed ice. Helsinki used to have a layer of packed snow/ice on the parking aprons during winter, which could be very slippery at times. A couple of pilots came a cropper on the turnround inspections there by slipping with their UK shoes, whilst all the locals used slightly studded boots.

If the terminal is down the far end of the airfield it might well be better to do a long slow rollout rather than vacate early onto a contaminated taxyway.

[av8boy]

I'm reminded of my days in ATC, long ago, at a location not so far from the current range of one Jerricho...

Braking action is poor and airport ops wants to get out on the runways to spread some urea. I approve it. Ops supervisor thinks it important to mention that it is "an extra stinky batch."

One of those useless things that sticks in one's head. :rolleyes:

[LatviaCalling]

Regarding mist in the cabin, this reminds me of a flight I was on in 1976 from then Leningrad to Moscow aboard a TU-104 -- the Soviet first commercial jet with a landing parachute which some little guy unhooked and collected at the end of the runway upon landing. It was repacked in the tail again before takeoff.

Anyway, back to the mist. Shortly after takeoff, from a rectangular hole in the middle of the cabin there appeared thick white clouds and the white knuckle passengers got even whiter. Some Russian women fainted from the so-called "smoke." Others had a hard time breating.

I asked what was going on and an FA told me, "Ah, I see they again put too much dry ice in front of the air conditioning fan." Otherwise, the flight was a little moist, but othewise uneventful.

[Flap 5]

Evening Star,

A soft landing on an icy runway with minimum spoiler is not a good idea. A firm landing giving you good contact with the runway with maximum spoiler to dump the lift is much safer. Of course if you land and kick off the drift perfectly then a soft landing is not a problem for directional control, but you do need to stop and for that you need braking action. If you have a cross wind a soft landing on an icy runway could actually be quite dangerous as directional control is lossed.

In fact if the runway is classified as 'icy' you are not allowed to land, according to most countries regulations (I don't know about Russia).