High winds at major airports?

[teleport]

Tried to do my homework on PPRuNe and came across these:
http://www.pprune.org/forums/showthread.php?t=44985
http://www.pprune.org/forums/showthread.php?t=260130

But they don't quite answer this: when will a major airport like LHR introduce restrictions due to the wind like during the recent fog mularkey?

Currently see winds 248 at 15 gusting 26.

[skydriller]

Originally Posted by teleport

Currently see winds 248 at 15 gusting 26.

Well, I can assure you that isnt so bad, as I have landed light aircraft in similar (but not at Heathrow!!), especially as Heathrow/Gatwick have East/West runways. I have landed in 25Kts straight down the runway with no problem whatsoever in a light aeroplane - I would not land in a 25Kt crosswind though. The real problem for light aeroplanes with higher windspeeds (say 30kts+) is really taxiing around when you have landed.

I dont fly heavy metal, so stand to be corrected, but I think you will find that similarly for Airliners, a constant higher speed wind is OK, depending upon direction relative to the runway (ie straight down the runway) but the real problem for pilots is gusting wind and the variable direction of the wind, or even both together !!! Obviously Airliner limits would be higher than for a light aeroplane though.

Regards, SD..

[teleport]

Thanks. But have airports got rules for strong winds like they do for fog re. increased distance between aircraft?

[TopBunk]

AFAIK there are no special restrictions because of high winds ..... however .... major airports will suffer reduced capacity with high winds down the runway axis. Normally they will separate similar aircraft by 2.5 to 3nm on final approach. Lets say you fly 180 kts to 8 nm final then 160 to 4 then reduce to final approach speed. Flying 180 kts in still wind will take you 1 minute to fly the 3 nm you are behind he preceding aicraft, with a 60 kt headwind your groundspeed will be 120 kts, so the 3 nm will take 1.5 minutes to fly. Hence fewer movements possible.

[timmcat]

Hope this isn't too off topic, but can anyone answer this (if there is technically anything wrong in my terminology, please be gentle with me).

Just dropped into my usual 'observation' spot at Leeds.

737 on very short finals to RWY32 - Instant wind checks 250 / 260 varying between 42 and 55 kts. Did a go-around - ATC asked his intentions, and the FO's reply was 'the captain says we'll have another go'. Came around for another approach, wind conditions the same (in the interim there had been a gust of 68kts), and despite the aircraft lurching violently from side to side, and the PIC taking off the 'crab' at the very last second, it landed successfully. Much hilarity on the RT between the flight deck and ATC whilst taxiing to the stand- the controller finally saying 'I've been here a lot of years and that's the best I've ever seen'.

My question - surely those conditions were outside limits? Does the airline dictate the limits, or the manufacturer, or the CAA?

[5150]

Aircraft published crosswinds are probably only demonstrated -

[teleport]

Got the argument re. headwind and lower ground speed. Then, is there a safe margin for higher air speeds and does commercial or military indeed do that?

[Rainboe]

As long as the crosswind was within company limits just before touchdown, there is no other wind limit that applies apart from the problem parking. High windspeeds can turn aeroplanes when parked, which can cause big trouble if attached to a towbar or on a jetty, so there is usually a limit on operations on the ground. At Leeds this summer, we unloaded the passengers on the jetty, but there was a sudden panic to get the aeroplane towed away and into wind in case it caused damage when swinging. Years ago we used to park a HS748 at Sumburgh, Shetland Islands. Some mornings I used to wonder whether it would still be there!
These limits vary with type, so airport operators do not close the airport- they leave the decision to pilots.

[Harves]

Timmcat,
I was said FO on the 737 you mention into Leeds today. The final windcheck we received was 260/42. To make our maths easy we used 2/3rds mean wind rounded up giving 30 knots. We had briefed this upper limit figure prior to approach (also in the case of the wind veering)so knew when to go around as in the first case. Company limits are 35 dry and 30 wet so worked well for us today.
That said, it was an interesting approach and I am sure quite interesting from the ground too. Certainly not an FO landing and for that I am glad. Captain did a great job though.
And yes indeed, we did have to park up into wind and still 35 odd tonnes was being blown all over the shop....quite a day.

[Right Way Up]

Just curious, but isn't 60 degrees off wind more like 9/10ths i.e 36 kts?

[TopBunk]

RWU

Technically you are correct. In practise, however, most pilots use he following rule, which avoids having to get out a calculator whilst wrestling with an aircraft down final approach:

Rule:

Crosswind component = windspeed x (degrees off runway heading/60)

This roughly mirrors the sine function; ie 30 kts @ 30deg off rwy heading = 30 x (30/60) = 15 kts across; or 30 @ 50deg off = 30 x (50/60) = 25 across.

When you are fighting the elements down the approach, you really don't have time to do other than 'ballpark' sums in your head, it's not a simulator up there.

[Right Way Up]

Topbunk, my post was a little tongue-in-cheek. I have done enough of my own interesting approaches in the last month or two, but ballpark figures should at least be in the park. 60 degrees is nowhere near 2/3 crosswind, and using your figures you would assume all 42 kts across. Anyway well done to the crew. I can imagine the approach would have been more than a little interesting.

[Harves]

Indeed RWU,
As TopBunk said, you are quite right. In different circumstances, I would be using 1.5 times the offset to give me my percentage and would indeed have had 90% of the mean wind. But as I said, 2/3 rds rounded upwards was easy at the time and as the wind was chaging so much (from 270/32 to 260/42 etc) with gusts making standard tasks difficult.....this worked for us in conjunction with the FMC which actually gave us 29 from the left just prior to touchdown. But your point is well taken as being accurate.
Cheers

[Spitoon]

To answer the original question - in the UK, airports generally do not place weather-related limits on take-offs or landing (the only exception that comes to mind is a vis minimum for take-off if the runway lighting is basic - or non-existent). Pilots are given the relevant information and will make an approch or take-off if their procedures permit it subject, of course, to the Captain's discretion.

[Dream Land]

The answer would be no, company SOP's and aircraft certification being the limiting factor.

[Kit d'Rection KG]

Originally Posted by Spitoon

...subject, of course, to the Captain's discretion.

Hmmm, not quite. This is an area where the commander (not the captain) has very little discretion; the requirements are laid out and he must simply know and (occasionally) interpret them. His only discretion would be to refuse to operate when he could have done, and for that, he would be answerable to flight ops management.

[timmcat]

Harves, many thanks for that insight.

Yes, it was interesting from the ground - just how close to the ground did the wingtip get on the very last rather violent 'wobble'?

And yep, in 20 years of watching from that spot - best I have seen too.

Apologies to the thread starter for the drift.

[Harves]

I am sure it had bags of clearance, our flight data monitoring prevents us hiding much...but you probably had the better view of that lol. Anyway, good to see you guys out there come all conditions, keep it up. It's very rewarding for us to give people some enjoyment, however, I tend to prefer the nice calm days, rare as ther are at Leeds.

[Spitoon]

Originally Posted by Kit d'Rection KG

Hmmm, not quite. This is an area where the commander (not the captain) has very little discretion; the requirements are laid out and he must simply know and (occasionally) interpret them. His only discretion would be to refuse to operate when he could have done, and for that, he would be answerable to flight ops management.

Well, it was said with tongue slightly in cheek but ultimately the commander, in discharging his many responsibilities (set out largely in the Air Navigation Order for UK purposes), exercises discretion - maybe that is where interpretation comes in. And yes, he or she will no doubt have to justify any decision not to do something that the 'book' permitted, but nonetheless, the commander has the authority to exercise discretion....just as I, as a controller, have had to explain in the past why I chose to follow a particular course of action that was not by the book. In my experience, if there is a valid reason for the decision there is no problem.

PS - I know the difference between Captain and Commander....it just didn't seem sensible to start using specific and not necessarily well understood terms when answering a question that was posed in a non-technial way. Well, that's my excuse anyway......

[Seat1APlease]

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