Hi,I am enroute to FAJS planned arrival is 03L length 14495ft Elevation 5558ft. Dont have my laptop and FCOM with me and need some help with the wind additives.Arrival winds are currently 010/17 knots gusting to 27 knots my Vapp is 168 knots as I will be arriving at MLW.Here's the confusion - from memory the additives are half the steady state wind plus the full gust, that would give me a Vapp of 186 knots?? so I'm sure I'm getting something wrong. I know the the MD11 lands fast at MLW and high elevation's but 186 sounds too high.Can anyone check this.Thanks

I made a quick Topcat performance calculation and this is what I got for the current weather:LANDING FAJS/JNB RWY 03L LDA 4418M PH-KPB MCDONNELL DOUGLAS MD-11 CF6-80C2D1FO R TAMBO INTL TEMP +16C QNH 1027 WIND 360/17 (14KT HW)-------------- INFLIGHT CONDITIONS -------------- ** 35/EXT ** DRY ** LDG MANUAL ** ** AIR COND ON ** ANTI ICE OFF ** ASSUMED LANDING WEIGHT 213869 KG VREF=160KT VAPP=172KT ---------------- MAXIMUM BRAKING ---------------- MANUAL 247892 KG 1588M (REM 2830M)-------------- AUTOBRAKE LDG DIST --------------- AUTO MAX 247892 KG 1778M (REM 2640M) AUTO MED 247892 KG 2215M (REM 2203M)//AUTO MIN 247892 KG 2600M (REM 1818M)***************************************************MAXIMUM STRUCTURAL LANDING WEIGHT IS 213869 KG***************************************************---------------------- END -----------------------As for your initial question the maximum additive is 20 knots.

Cheers mate,I also use Topcat, you answerd my question with Max additive of 20 knots :) I've checked the arrival weather and the winds are back to a steady state of 17knots but the TAF predicts 18knots gusting to 28 knots. Will see what happens when I arrive in the next hour.Thanks again

The formula for VAPP is.VREF+1/2 Wind+(Gust-Wind).So with speeds of VREF=155 Wind:100/16G25KT it would be.VAPP=155+8+(25-16)VAPP=155+8+9So VAPP=172 in that scenario.Hope this helps.Kevin W Forgot to add Minnimum VAPP= VREF+5

Exactly right Kevin, My mistake was adding all that to the Vapp instead of the Vref therefore getting an extra 5 knots so I was landing at 177 knots.Well the landing went well so thanks for the help everyone. I dont get to sim much these day's so my last flight will be FAJS - EDDK The high field elevation should make for some interesting T/O perfomance calculations with TOPCATRegards

Exactly right Kevin, My mistake was adding all that to the Vapp instead of the Vref therefore getting an extra 5 knots so I was landing at 177 knots.Well the landing went well so thanks for the help everyone. I dont get to sim much these day's so my last flight will be FAJS - EDDK The high field elevation should make for some interesting T/O perfomance calculations with TOPCATRegards

Just for the record:The correct way to calculate Vapp for the MD11 can be found in the FCOM Performance Data section.Page PD.00.1 gives notes (1 & 5) how to do this.Sorry for Kevin and TOPCAT that use the -400 like way to calculate.[[so with speeds of VREF=155 Wind:100/16G25KT it would be.]]For me its 155 + 9 = 164Regards,Harry

Just for the record:The correct way to calculate Vapp for the MD11 can be found in the FCOM Performance Data section.Page PD.00.1 gives notes (1 & 5) how to do this.Sorry for Kevin and TOPCAT that use the -400 like way to calculate.[[so with speeds of VREF=155 Wind:100/16G25KT it would be.]]For me its 155 + 9 = 164Regards,Harry

Ok lets get to the bottom of this :) I have my FEDEX FCOM back and this is what it says.Wind Additive: Greater of 5 Kts, 1/2 steady State Wind > 20 Kts, All the Gust Factor...I can see you added the full 9knots gust to Vref 155 does the above imply I shouldn't add anything else unless the steady state wind is above 20 Kts? That doesn't sound safe.Regards

Well the FEDEX FCOM is missing half steady state wind 'Or' full gust. You dont add both.Thanks for your help and the PMDG FCOM!

Sorry for Kevin and TOPCAT that use the -400 like way to calculate.

I got my formula directly from an American Airlines MD-11 FCOM. Kevin W

I got my formula directly from an American Airlines MD-11 FCOM. Kevin W

My KL MD11 FCOM calls the Additive WCF (Wind Correction Factor)Vapp = Vref + WCFThe WCF is the greater of 1/2 windspeed above 20 kt OR full gust.Minimum 5 kt and maximum 20 kt.The name being different, it is the same calculation as in the PMDG FCOM.Fly safely.Regards,Harry

I guess this proves any formula is a good formula if it provides for a safe landing, and keeps you within limits of min: VREF+5 - max: VREF+20. And from what I've learned you can never be wrong if you just follow what the books say.Kevin W

Here's the confusion - from memory the additives are half the steady state wind plus the full gust, that would give me a Vapp of 186 knots?? so I'm sure I'm getting something wrong. I know the the MD11 lands fast at MLW and high elevation's but 186 sounds too high.

The thing you are probably missing here, is that the formula which gives you that speed is intended to deal with strong winds right from the start of the approach. But you are descending through those winds, down through a gradient, where the wind speed reduces as the friction with the terrain slows it down. So that's generally the correct speed for the start of your approach, but not necessarily the correct speed over the piano keys.For many airliners, the above rule of thumb has the caveat that a maximum of 20 knots should be added to the bug speed, and you would normally be five knots over that anyway coming down the pipe until committed to the landing, so only the gust factor should be considered when at touchdown, because the wind will have dropped as you descended through the gradient. Recommendations vary for different airliners, but the fall-off of the wind gradient is often something people forget.Al