Approach / Touchdown Speed

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SpeedWeasel
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Approach / Touchdown Speed

Post by SpeedWeasel »

Here’s another one for you guys to discuss. Until recently I believed that when approaching to land in gusty wind conditions you adjusted your VRef to be VRef + half of the wind gust. i.e. VRef = 120kts and the wind is 20kts gusting 30kts the new VRef would = 125kts.

Our company policy is to approach at and cross the fence (50ft.) at VRef + 10 then slow to VRef for touchdown.

It was recently suggested to me that VRef is VRef and doesn’t change and that it should only be the approach or target speed that would be adjusted for wind gust, just wondering if anybody had any thoughts on the subject.

Thanks

SW
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pika
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Post by pika »

Vref is always Vref as it is based on landing weight. Vapp will change based on winds. Typically carry the adjusted approach speed to the flare and bleed it off to Vref+5 for landing. Standard correction is half of the wind speed plus ALL of the gust. So in your example half of the wind speed is 10 knots and all of the gust is a further 10 knots.
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Thump
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Post by Thump »

I think people are mixing up the "as a general rule" with fact for any a/c.

I feel it differs, your light twin is affected differently then your medium turbine would be, in fact it will be differnt from type to type.

The extra speed should make you more stable but also should give you the extra control authority in case you get blown sideways, I think we will all agree on this. I feel that in general (some planes just don't land well fast) in very guisty conditions if you can, keep the higher speed all the way till touchdown.
BUT that is the point of sop's, they were (hopefully) written by guys (or girls) that know your a/c and have figured out the best way to battle with your ship.
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.80@410
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Post by .80@410 »

Higher speed till touchdown ? Uh uh :oops:

What's the increased landing distance based on each 5 knots increase in Vref ? I can't remember off the top of my head, but imagine that the wind is 22 gusting 40.......that means ( based on the standard all the wind and 1/2 the gust a 20 knot addition to your speed. Your landing distance would be somewhere in the neigbourhood of 50 % more !! :shock:

Hold it to the fence ( 50 ft ) and then bleed it off.

.80
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chewsta
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Post by chewsta »

Hows this for a comparisson:

DA20 Katana Vref+1/2gust
B767 Vref+gust+1/2windspeed

Depends on the a/c type methinks. :?:
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Thump
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Post by Thump »

.80 Like a said though :x , all depends on so much, ok assuming you have enough runway why waffle around at a slower speed, you leave yourself soo vunerable to being kicked around...
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RB211
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Post by RB211 »

Your landing distance increase is not that simple, .80. The speed added to Vref is, of course, airspeed while your landing distance is actually a function of g/s.

In your scenario, adding the 5kt to Vref in still wind conditions will increase landing distance. Adding 5kt into a 10kt headwind could leave you with a shorter distance.

The 75/76 are typically a final approach speed of Vref + 5kts in any wind for an autoland. If flying any part of the final approach manually then it is Vref + 1/2 the headwind + all the gust to a max of Vref + 20.
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oldtimer
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Post by oldtimer »

One thing to remember is that Vref is in fact 1.3 times the stall speed in landing configuration. Except that if the airplane is "legal" to land with various flap settings, (almost all are) then Vref can be calculated for the various flap settings so if you are flying a Metro and decide to land with 1/2 flap, then Vref is 1.3 times Vs 1/2 flap. The accepted rule of thumb is to increase Vref by all of the wind plus 1/2 the gusts to a maximum of 20 Kts. When the manufacturer calculates the effect of wind on landing performance, he uses 50% of the positive(reduction) effect of a headwind and 150% of the negative effect of a tailwind. Fly the airplane on a 3 degree descent profile or glideslope at Vref plus the wind to 50 feet, bring the power to idle and flair once. If the airplane does not land, fly it on. The best for a gusty bumpy day is to become familiar with the attitude and power required to achieve the performance and set that. The wind will slow your ground speed, so you have to adjust your descent profile to accomodate.
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pika
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Post by pika »

10 knots fast on the touchdown in a 757 adds an extra 400' to the landing.
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RB211
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Post by RB211 »

pika wrote:10 knots fast on the touchdown in a 757 adds an extra 400' to the landing.
Are you saying the Boeing Flightcrew Training Manual is detailing incorrect procedures?

Again, 10 kts 'fast' is different than a planned increment for given conditons.
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Always Moving
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what are we discussting

Post by Always Moving »

seams to me that every plane is diferent.
So I read the MANUAL
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pika
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Post by pika »

I'm not saying the BFCTM is doing anything incorrectly. All I'm stating is a piece of Boeing information. Tryed to find the exact reference but I can't find it in the BFCTM so I'll have to keep looking.
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Bede
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Post by Bede »

The high ups at hte company I fly for want us to approach at Vref+10, then slow to Vref after minimums to be at Vref at 50' then slow to Vref-10 for TD. This is in a light turboprop (MU2). I have always been taught to be stabalized at Vref during the final approach. I think that the FlightSafety Foundations suggestes stabilized approached by 1000' in IMC. They recommend you be at Vref -5/+10. The high ups believe in a slow deceeleration from Vref+10 at 200' to Vref-50 at TD. The argument is that if you miss and lose an engine during the GA, the extra 10 kts will come in handy since we retract the flaps to 5 at 120 kts. Any idea's?? Does anyone else in bigger/similar size aircraft do this??
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