Hi. I would like to know if a bad snowing runway with brakeeff for instance is 0.68 would make any different to vapproch speeds and landing speeds at all? I dont see any on the page in the fmc as you do see.it on the takeoff page 2. Which gives you a slighter lower V1 off cause with wet or sloppy weather. How do you calculate the amount of brake vs runway lenght on landing otherwise with the example above? Thanks Michael

 

Btw. Do real pilots have a easy to use wind correction speedtabel or is it by sextant in the cockpit?

Hi. I would like to know if a bad snowing runway with brakeeff for instance is 0.68 would make any different to vapproch speeds and landing speeds at all?

 

Btw. Do real pilots have a easy to use wind correction speedtabel or is it by sextant in the cockpit?

 

No change to Vspeeds, which are based on weight of the aircraft and it's relitave stall speed in landing configuration. Just because the runway is wet or icy doesn't make the aircraft stall at a lower speed (infact with icing there may be an increase in stall speed).

 

The only real change to the Vspeed will be during gusty wind conditions. When there is a high gust component (ie the wind is 6 knots with gusts of 25 knots) then there is a 19 knot difference between the highest windspeed you will encounter and the lowest windspeed.

 

This may impinge on the stall speed in some situations, so you speed up the approach speed.

 

If there was no gust, you fly the final approach at Vref + 5... so a 138kt Vref means you fly the final approach (till before flare) at 143kts. When you hit 30ft, you pull thrust to idle and flare, when done right, the flare will reduce speed by 5kts before touchdown (exactly at Vref).

 

A general rule of thumb I'v heard is that in gusting wind conditions, add half the gust component to Vref. If that gust component is less than 5kts, you use 5kts, if it is bigger than 5kts you add the half gust component.

 

so in the example above, there's a 19kt gust component (6kts is the lowest windspeed, 25kts is the highes).

 

half of 20kts is 10kts. minus half. Therefore I'd fly Vref+10 on this approach.

 

138kts Vref (as per FMS)

 

Approach speed 148kts.

 

Now if the stuff is Icy, you need to look at the runway length. A quick glance at the braking distance tables (in the PMDG manuals, ftw) to make sure it will actually stop at this speed in the landing distance available, select your autobreak, etc.

 

If the runway is contaminated I'd be looking at a flap 40 landing which is the best you can do for a slow approach. Slowing down below Vref puts you in vicinity of Stall and is unsafe.

 

So in summary:

 

Constant windspeed at airfield = Vref+5

(even if wind is 250/60kts but no gust component, fly the approach at Vref+5)

 

With Gust = Add Half of the gust component to Vref (ie 5kts gusting to 15kts = Vref+10, 5kts gusting 10kts = Vref+5)

 

Vref is calculated by the FMS based on weight, and planned flap setting. It has nothing to do with wind or runway length.

 

If after looking up your landing speed + landing distance available on the braking distance table, and find that your estimated braking distance is bigger than the runway, you're gonna have to go somewhere else with a bigger runway.

Hi,

Examples about corrections applicable at Vref due to gusting winds are reported into Flight Crew Training Manual...

 

Merry Xmas!

 

Andrea Buono

No change to Vspeeds, which are based on weight of the aircraft and it's relitave stall speed in landing configuration. Just because the runway is wet or icy doesn't make the aircraft stall at a lower speed (infact with icing there may be an increase in stall speed).

 

The only real change to the Vspeed will be during gusty wind conditions. When there is a high gust component (ie the wind is 6 knots with gusts of 25 knots) then there is a 19 knot difference between the highest windspeed you will encounter and the lowest windspeed.

 

This may impinge on the stall speed in some situations, so you speed up the approach speed.

 

If there was no gust, you fly the final approach at Vref + 5... so a 138kt Vref means you fly the final approach (till before flare) at 143kts. When you hit 30ft, you pull thrust to idle and flare, when done right, the flare will reduce speed by 5kts before touchdown (exactly at Vref).

 

A general rule of thumb I'v heard is that in gusting wind conditions, add half the gust component to Vref. If that gust component is less than 5kts, you use 5kts, if it is bigger than 5kts you add the half gust component.

 

so in the example above, there's a 19kt gust component (6kts is the lowest windspeed, 25kts is the highes).

 

half of 20kts is 10kts. minus half. Therefore I'd fly Vref+10 on this approach.

 

138kts Vref (as per FMS)

 

Approach speed 148kts.

 

Now if the stuff is Icy, you need to look at the runway length. A quick glance at the braking distance tables (in the PMDG manuals, ftw) to make sure it will actually stop at this speed in the landing distance available, select your autobreak, etc.

 

If the runway is contaminated I'd be looking at a flap 40 landing which is the best you can do for a slow approach. Slowing down below Vref puts you in vicinity of Stall and is unsafe.

 

So in summary:

 

Constant windspeed at airfield = Vref+5

(even if wind is 250/60kts but no gust component, fly the approach at Vref+5)

 

With Gust = Add Half of the gust component to Vref (ie 5kts gusting to 15kts = Vref+10, 5kts gusting 10kts = Vref+5)

 

Vref is calculated by the FMS based on weight, and planned flap setting. It has nothing to do with wind or runway length.

 

If after looking up your landing speed + landing distance available on the braking distance table, and find that your estimated braking distance is bigger than the runway, you're gonna have to go somewhere else with a bigger runway.

You spent a lot of time looking into this. I'd go with Andrea - you might check the FCTM. I think it has some different suggestions. All Gust + Half Steady State HW, etc.

You spent a lot of time looking into this. I'd go with Andrea - you might check the FCTM. I think it has some different suggestions. All Gust + Half Steady State HW, etc.

 

Try that with wind 25kt gusting 40kt in a 737-800

 

Flap 40 Vref 138kts

138 + 32 = 170kts

 

So your Approach speed will be higher than max speed for flap 40. and 170 knots. Good luck wiping 30 knots off your speed in the flare... actually good luck wiping 30 knots off your speed from Outer Marker to touchdown!

 

The gust is the important part. It's how much your (air) speed will vary as the winds gust.

 

But sure, shoot a flap 40 approach at 170kts if you want.

According to B737 FCTM 1.11:

 

"If the autothrottle is disconnected, or is planned to be disconnected prior to landing, the recommended method for approach speed correction is to add one half of the reported steady headwind component plus the full gust increment above the steady wind to the reference speed. The minimum command speed setting is VREF + 5 knots. . . .

 

When making adjustments for winds, the maximum approach speed should not exceed VREF + 20 knots or landing flap placard speed minus 5 knots, whichever is lower."

 

Some recommend the method described by Trent with smaller aircraft.

Try that with wind 25kt gusting 40kt in a 737-800

 

Flap 40 Vref 138kts

138 + 32 = 170kts

 

So your Approach speed will be higher than max speed for flap 40. and 170 knots. Good luck wiping 30 knots off your speed in the flare... actually good luck wiping 30 knots off your speed from Outer Marker to touchdown!

 

The gust is the important part. It's how much your (air) speed will vary as the winds gust.

 

But sure, shoot a flap 40 approach at 170kts if you want.

That's part of the "etc." I wasn't going to quote the whole section. Most pilots don't use F40 in gusty conditions, but what do I know. . . :lol:

That's part of the "etc." I wasn't going to quote the whole section. Most pilots don't use F40 in gusty conditions, but what do I know. . . :lol:

 

Which now puts Vref at 141, and your approach speed at 173kts.

 

Considering 160kts to the Marker is a rather common ATC instruction...

Just popping by into this thread hopskip, but the issue of having to be bleeding off 30 knots in the flare is not a concern in the example you use above if you stick with the FCTM. So in your example above, if VREF is 138, approach at 158 and touch down at 153 because the FTCM says to maintain the full gust component.

Okay Thanks a lot guys. I will for sure look into the brake tabel. Would love someone to explain a snowy and icing METAR with all the information regarding this incl rvr.

 

Your answers might explain my landing speeds yesterday in copenhagen were winds was 25knots gusting to 40knots. I was given a vapproach speed with flaps 30 at 144 and i only did add 8 knots to this. I did a automatic flare land without the precense off a land 3 and it approach at 166-168 knots

 

Michael Moe

Your answers might explain my landing speeds yesterday in copenhagen were winds was 25knots gusting to 40knots...I did a automatic flare land without the precense off a land 3 and it approach at 166-168 knots

 

That might compound any issues you might be experiencing....dependant on the wind direction & strength relative to the RWY HDG it could result in a cross-wind condition beyond the Autoland capability of the aircraft.

 

Better to fly manually under those types of conditions with the VAPP adjusted using the formula (as highlighted by others) in the FCOM.

 

Those AUTOLAND Limitations are covered here .....

 

PMDG-NGX-FCOMv1 Limitations L10.5 (pp 57-58)

 

 

That might compound any issues you might be experiencing....dependant on the wind direction & strength relative to the RWY HDG it could result in a cross-wind condition beyond the Autoland capability of the aircraft.

 

Better to fly manually under those types of conditions with the VAPP adjusted using the formula (as highlighted by others) in the FCOM.

 

Those AUTOLAND Limitations are covered here .....

 

PMDG-NGX-FCOMv1 Limitations L10.5 (pp 57-58)

 

 

 

 

 

Thanks for the shortcuts. yesterday the wind wad only 3degree off rwy heading so it was pretty much headwind. Dont know if autopilot would normally disregard the fmc vapproach page and desicition here but 152 to a 168 is a pretty big gap.

 

Michael Moe

 

 

Which now puts Vref at 141, and your approach speed at 173kts.

 

Considering 160kts to the Marker is a rather common ATC instruction...

If it's gusty, you'd probably use F30 and then your maximum approach speed would be 170kts (placard-5). If ATC assigns something less, you say, "Unable."

 

There is no correction for wind/gust if you're doing an autoland. (At least not for fail-passive - not sure about fail-active.) You still need to stay within the limitations.

Try that with wind 25kt gusting 40kt in a 737-800

 

Flap 40 Vref 138kts

138 + 32 = 170kts

 

So your Approach speed will be higher than max speed for flap 40. and 170 knots. Good luck wiping 30 knots off your speed in the flare... actually good luck wiping 30 knots off your speed from Outer Marker to touchdown!

 

The gust is the important part. It's how much your (air) speed will vary as the winds gust.

 

But sure, shoot a flap 40 approach at 170kts if you want.

 

At least at my airline it is half the steady state wind plus all the gusts up to a maximum of 20 knots additive. And that is only if the auto throttles are disengaged. If you leave them on there is no wind additive.

I know this is SOP-dependent (as Andrea, Matt and Tom have mentioned), but I think it's worth mentioning that the end call for your flight simming (absent SOPs written for you) is in the FCTM.

 

Take a look there for that final answer, use that, and we can all go home happy.

 

I know...me...telling people to go take a look at the manual...surprise!