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JSACKS

What is the right approach speed in a t-storm ?

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Today I landed the PMDG 744 in a major t-storm at KIAD. My Vref25 was 149. Cross wind was 18k gusting 28k. Turbulence was "severe." I set the MPC SPD to 159 but felt it was a little slow in the awful conditions. Interestingly, I observed the AT drove the speed to around 160-162 for much of the approach until below 500'.What should the approach speed have been for a flaps 25 landing and how did you calculate it ?Appreciate any replies as I am still a bit unsure about adjusting for crosswinds and gusts. And turbulence of the kind I had today adds another factor that I just don't know how to deal with accurately. I just aim for an approach pitch of anywhere from flat to 2 deg in this kind of weather and aim to land at Vref+a few knots along with some positive N1 as well before pulling back on the thrust and hitting reversers with nosewheel still in the air. Thanks!JS

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I don't know about the 747, but I took a sim course on the CRJ in school and we flew approaches at Vref + 5 and any time there was a gust factor we added half of that gust factor, but not more than 7 knots additional. In your case, you had a Vref of 149, so add 5 regardless, and then half of the the 18 to 28 gusts is 5, for a final approach speed of 159.

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A few things for you.First a simple chart (MD-80 AOM) for determing crosswind component, etc.:http://forums.avsim.net/user_files/162891.jpgOnce landing flaps have been established, target speeds (under stable air conditions) will be VREF + 5 knots. However, the decrease in wind velocity approaching the surface of the earth has the effect of a decrease in airplane velocity. Consequently, caution must be exercised to prevent airspeed bleed off and increased sink rate during the last stage of the approach.Target approach speed is VREF + 5 knots for landing in reported winds of zero to 10 knots. When landing in higher wind conditions (above 10 knots), add 1/2 the steady wind and the full value of the gust (if any). The total wind additive should not exceed 20 knots.So for your example, 1/2 steady winds (18kts) = 9, + all gust (10kts) for a total of 19kts additive, giving you an app speed of 168kts ! Just under the limits.I hope you find this helpful. I don't mean to be short, but I guess I'd rather have you ask more questions if need be, than overwhelm you with a bunch of data you don't need/want.

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The correct answer is to either hold until the worst has passed or divert. Even the big boys do their best to avoid severe convective activity. Especially during landing and departure phases of flight.

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I was going to say the same thing. The best approach speed in a TRW is to get the **** out of there as soon as you can. We were taught in training that TRW stands for The Rowdy Widow-maker. Don't respect her, just stay away from her.John M

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Certainly can't argue with any of this advice, I was just trying to answer the technical side of his questions.

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Brian:Thanks. Much appreciated.To others: yeah landing in a direct t-storm is foolish but hey it's FS so why not push the envelope to the limit....and beyond ? It's a great sim and the PMDG 744 is a great add-on!JS

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I know you were, I was just being "smart". Your information is informative and correct. JSacks posts below that this IS just a sim and I agree what better place to see what situations pilots can get themselves into and, hopefully, out of then in a simulator. When I was a flight instructor years back, we relied heavily on simulators to put our students in all kinds of awfull situations just to see how they would react. Makes we wish we could produce real microbursts,low altitude windshears and other dangerous weather phenomenons is FS9. Lets see someone land the Piper Cub on a dirt strip with a 25K crosswind component and winds gusting from 15 to 40K. Now that's flying!!!! John M:-beerchug

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Ah, if it were only that simple. If you are flying commercially, if the airport is open, you are going to do your best to land that plane. AND if other airlines are getting their aircraft down, so will you.I can recall trying 3 times to get into KBUF with the windshear warning going off each time as well as severe cross winds on approach and having to go around. The captain made the decision that we'd divert if we didn't make it the third time. We came in crabbed to the right so badly that the FFA (first flight attendant) said that she could see the runway by looking out the main cabin door's window. The captain kicked here out of crab at 10 feet, slammed her to the runway at VREF +15 (not a typo), slammed full reverse thrust and max braking and while the passengers were gasping in the back, it was the most beautiful landing I've ever seen and I silently thanked GOD that it wasn't my leg. To make a long story short, yes the final decision for the safety of the aircraft belongs to the captain. But part of his decision is what he will tell ops when he volutarily diverts or requests a hold when other airlines or company aircraft have landed their aircraft and the airport is still open for business.As far as avoiding convective activity, that's quite easy enroute...a mere request for deviation, but at airports like KMCO, KIAH, KDFW, KMIA, KIAH, KDEN in particular that get nasty convective activity spring, summer and fall...its those days that you earn your paychecks.

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Hi Mike,Ever fly the visual RW 19 at KDCA (the River approach) on a convective day? That's another paycheck earner.John M

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Heck yeah, I love River Visual at KDCA as much as I love River Visual at KLGA. Both are challenging when everything is VFR and light winds. But, add some shifting winds on final and add a few more knots to VREF and then figure out whether to bank the aircraft more steeply or drift a bit and bring her back over the threshold while still applying rudder. LOL.You want to see some consistantly ugly landings? LOL. My only regret is that I've never had a chance to fly the Parkway Visual to 13L/R at KJFK since Continental didn't fly into JFK at that time (I think they do now but with ERJs). When I was much younger we'd sit in the landfill at Jamaica Bay and watch the heavies fly it every day and it was always my dream.

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