Windy weather 17/01 - groundspeed on approach?

[treadigraph]

Group of us in the office are looking at the Heathrow approach out of the window (now that the sky has cleared a little!), watching a BA 747 appearing to c-r-a-w-l down the glide slope - assuming the forecast windspeeds of gusts to 70mph (or Kts?) are accurate, we are wondering just how slow the groundspeed would be today...?

Treadders

[HEATHROW DIRECTOR]

A/c on final approach to Heathrow usually fly around 160kts airspeed. Groundspeed will be considerably slower if there is a headwind although the effect on the aircraft will vary depending on the direction of the wind.

As I write the wind speeds on the approach to Heathrow are over 60 kts so aircraft may be flying the approach at not much more than 100 kts, or around 90mph.... with most of the M4 traffic overtaking them!!!!

[GANNET FAN]

Looking out of the 8th floor window in the City just now, watching the line of 3 aircraft heading west, it almost looks as if they are hanging in the air, their forward progress is clearly slower with these winds.

[treadigraph]

Thanks HD, the difference in speed is really quite marked compared to less windy days - which shows that I spend too much time looking out of the window on clear days rather than at my PC! It's more or less overcast again now, so back to work... :}

[Georgeablelovehowindia]

Latest LHR windcheck is 270 at 40 gusting 57. OK straight down the runway now - it was 230 earlier, of course - but still quite challenging due to the windshear on final. Still some go-arounds.

100 knots groundspeed equates to 115 mph and if somebody is doing that down the M4, they're (a) running the risk of getting airborne themselves and (b) grabbing the attention of the folks in the blue and yellow checked Volvo!

I wonder what it's like in the new control tower? :uhoh:

[Groundloop]

As I write the wind speeds on the approach to Heathrow are over 60 kts so aircraft may be flying the approach at not much more than 100 kts, or around 90mph.... with most of the M4 traffic overtaking them!!!!
Conversion the wrong way round? 100 kts more like 115 mph.


Just beat me to it, G-ALHI!!

[slingsby]

I would have loved to speed checked the pigeon who past my office window earlier, I would not like to have been on the receiving end of a departure from controlled flight,,,,, yeuk

[HEATHROW DIRECTOR]

Sorry for getting speed conversion wrong - put it down to age!!

[PPRuNe Pop]

Personally Bren, I wouldn't have mentioned it! :E :D

[runawayedge]

Pardon me for butting in......if the wind on the ground is at 60kts, chances are it will be considerably higher aloft.....on finals that could be anything up to 100kts......meaning groundspeed of about 66mph........chances are flashing blue lights in rear mirror are not for you!

[Geffen]

Around noon 4 thousand foot wind at LL 260/90

[Flightman]

A/c on final approach to Heathrow usually fly around 160kts airspeed. Groundspeed will be considerably slower if there is a headwind although the effect on the aircraft will vary depending on the direction of the wind.
As I write the wind speeds on the approach to Heathrow are over 60 kts so aircraft may be flying the approach at not much more than 100 kts, or around 90mph.... with most of the M4 traffic overtaking them!!!!

Real basic question here, so apologies, but we were discussing it in our office today, and no-one had the answer.

Using HD's numbers above. If the aircraft is doing 100kts, and the 60kts headwind makes it up to 160kt, what happens if the wind just stops? Most people said the a/c would just fall out of the sky! I argued that wasn't safe, couldnt be the procedure and the aircraft must be flying " in a 160kt config"
( for want of a better phrase ) and if the wind just stopped, it would still be doing 160kt, but also 160kts over the ground. Am I right, wrong, or mad? :{

[Right Way Up]

Flightman, what you describe is called windshear. A loss of 60 kts would indeed lead to "falling out of the sky". Unlikely though to be anywhere near that magnitude.

[point5]

The KLm F50s inbound to LL today showed a groundspeed of 55kts! Naturally a B744 was shuvved right up its ar:mad: e!

[Noah Zark.]

There was a nice clip on the Beeb news of a 146 taking off from somewhere with a significant crosswind. Fine bit of filming, and flying!

[NWSRG]

Take an approach speed of 160k airspeed. Into a headwind of 60k this equates to a ground speed of 100k. And at touchdown, a ground speed of say 80k for an airspeed of 140k...

Now, given that touchdown is therefore at about 60k less than normal, is there any procedure that allows a reduced flap approach in high winds...ie. less flap, higher touchdown airspeed, but offset by the wind. Say an airspeed at touchdown of 180k, equal to ground speed of 120k due to the wind...still a lot less than a 140k normal calm touchdown.

I remember a windy approach into BFS on an Easy 319 where the pilot seemed to adopt this approach...and the lesser flap seemed to allow a more stable approach as well...

[Rainboe]

In February 1990, there were 4 separate 100mph (aloft) gales sweeping through the south of England in the 4 weeks, all with westerly winds. I remember looking at the Omega groundspeed on approach into Gatwick several times to see just over 60 kts groundspeed. It made for very long duration approaches!

[1DC]

Departed Glasgow in a Shorts 360 in a full gale one night and when airborne we seemed to be flying over the runway at walking pace. We then flew to Teeside with the wind astern and the pilot said we made the journey 15 minutes quicker than he had ever done it before.

[NudgingSteel]

Real basic question here, so apologies, but we were discussing it in our office today, and no-one had the answer.
Using HD's numbers above. If the aircraft is doing 100kts, and the 60kts headwind makes it up to 160kt, what happens if the wind just stops? Most people said the a/c would just fall out of the sky! I argued that wasn't safe, couldnt be the procedure and the aircraft must be flying " in a 160kt config"
( for want of a better phrase ) and if the wind just stopped, it would still be doing 160kt, but also 160kts over the ground. Am I right, wrong, or mad? :{
As RightWayUp says, that effect is called windshear. It's defined as a sudden change of wind speed or direction, that occurs significantly faster than the aircraft can accelerate or decelerate. As you say, if an aircraft was at 160kts airspeed into a steady 60kts headwind, it would be moving forwards at 100kts groundpeed. If the wind suddenly stopped, the aircraft would still be moving over the ground at 100kts (because it's a big lump of metal that has a lot of kinetic energy which remains the same for the next few moments) but the airflow over the wings is suddenly only 100kts...which is bad news until the aircraft can increase thrust and accelerate back to required airspeed. For an airliner, you're right, that would almost certainly lead to a stall. Fortunately the wind doesn't ever just suddenly and completely stop!
In the UK, windshear is rarely of such a large magnitude. (It's often encountered at an inversion layer). I had traffic report a loss of 40kts in turbulence on short final a couple of weeks ago as a squall was passing through, but that's the largest I've ever heard of here. Usually it's a variation of about 20kts maximum, up or down. If windshear is reported or predicted, crews will add an amount to their final approach speed to allow for the effect described above. It can go the other way; positive windshear suddenly increases airspeed and can cause the aircraft to 'balloon' or climb.
It's a bigger problem in places like the USA with the huge thunderstorms that can occur there, and microbursts can cause severe windshear effects many, many miles away from the storm.

[Dufo]

~40kts GS on short final to EGNS 21, done with a L-410.
And 25kts GS just before stalling over IOM VOR on a proficiency check a few minutes before, with the same a/c.

[Midland63]

Methinks the old airspeed (and does it make a difference if it's indicated or true?) vs groundspeed confusion permeates this thread.

Would someone more articulate than me like to give the definitive explanation keeping the effects of windshear for Lesson 2?

Rainboe? (I'm glad to see you post on Spotters' Corner - as a "spotter/SLF" myself, I will pay more attention to this board from now on.)

:O

M63

[Groundloop]

Remember in days gone by at Glasgow if busy, ATC often used to turn Loganair Islanders into wind and leave them for a while. They didn't move!

Don't know if they still use this trick.

[Rainboe]

In the early days of the Fokker F28, I saw one take off at Frankfurt. Listening in on the ATC frequency, I suddenly heard the controller call it, with a desperate note of urgency in his voice, with 'say airspeed immediately!'. The very cool pilot called back about '50 knots'. The controller said 'what are you doing? Do you have an emergency?' and the pilot said 'negative! We are doing stalling demonstrations for a customer'. I suppose if he turned towards the wind and got the speed back like that, he'd virtually stop over the ground and appear on radar as a stationary point!

Midland
Rainboe? (I'm glad to see you post on Spotters' Corner
Where'd you think I came from too?

[Mister Geezer]

Going into Brussels a couple of weeks ago there was very strong westerly winds and the groundspeed was as low as 64 knots on the ILS. IAS must of been 115 - 130 ish - took ages!!!

[Maude Charlee]

I'm sure I had a man on a horse ride past on the approach into Galway recently - 57kts GS with 90kts on the nose at 2000'.

[BOAC]

Is it time to tell again the story of flying a circuit backwards in a Chipmunk?

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BOAC, yes please do!

[Rainboe]

We want the 'flying backwards in a chipmunk' story, preferably embellished with 'nothing on the clock but the makers name' angle inserted.

[treadigraph]

Inserted or inverted?

[BOAC]

Oh! alright then:) but only if you tell us about Tridents:mad:

It is nice to have 45 kts at 1000', get airborne with lots of welly. At 500', bring speed back with power on to near stall and bank to downwind leg (still pointing in take-off direction.)

Fly d/wind leg backwards - make call 'downwind' and hear quizzical note in controller's voice.

At end of leg, bank towards final, and apply power and increase speed to make the approach.

Easy, innit?

Come on - who has NOT done it?

...........nearly forgot - 'nothing on the clock but the makers name' and I'll leave details of the insertion for another forum.

[treadigraph]

I remember hearing about a Rallye display at the Biggin Hill Air Fair many moons ago, in a gusting wind which enabled the pilot to indulge in some gentle reversing. During the subsequent very slow flare to land, the wind - capricious as ever - dropped considerably as did the Rallye, requiring some rather expensive (in old money) repairs.

[Midland63]

... but only if you tell us about Tridents:mad:


Oh, Rainboe please give this 40-something "spotter" (I prefer the expression "interested third party") a Trident story or two!

My love affair with the Trident began in the early 70's when my Dad buttoned a Captain Quilley at Edinburgh - Turnhouse then - for a few comments for my school project - high terrain and the need for the booster to get the T3 off the old runway, I recall he said.

Also, doing a complete double take at Heathrow seeing the preserved one in BEA colours while the bus was stopped while a 777 was towed across the road!

Thanks, M63