Thats where that mental math comes in handy....

 

Deltas 55 wind check!

 

Well it's in the May 737 Fleet Newsletter for one, not sure where else to find it if you're not lucky enough to be on the 737.

Specifically they say "the amount of tw is now capped to preserve RATOW margin above RMWT/TOWT. The max tw displayed will be set to TW00 when the rwy hdwind component is 5 kts or greater."

The article continues with more information, but that seems the most relevant to our discussion. At first I was happy about going to the PLW because it seemed simpler, but flying today and checking our WDRs and seeing they all had TW00 on every line I'm concerned.

So I guess the idea is to have a larger weight buffer at the expense of having ANY tw protection? Aren't we just trading one problem for another? And a problem that requires you to:
1. Hear ATC say the winds when all you're listening for is "cleared for T/O" and
2. Do quick mental math and realize you now have as little as 1 kt of TW making the T/O numbers invalid

And as others have already mentioned the ATIS could be saying 5 kt hdwind all day long but all the matters is tower gave you a wind read-out with a tailwind.

 

Basic trig, actually. Not hard. But I'm sure you knew that.

 

There is a $0.99 (yes, exorbitant by pilot standards) app in the App Store called 737 approach speed that has saved my bacon several times with late, changing wind calls. I like that it has pictures and that I can set the runway heading and then drag the wind line to wherever, set velocity and gust, and voila, that quartering tailwind with mild gust at LAX is out of limits for landing. YMMV

 

The problem is the system only looks at the HW/TW component. For a hypothetical RWY36, winds 08015 are a 3kt headwind, so the WDR spits out TW02 (current wind component minus 5). We all know how easily that can swing to 10015 from tower, and now you have a 3kt tailwind and a canceled takeoff.

I like the new procedure because it's intuitive. I personally haven't run into the tailwind issue, but I'm sure the program will be tweaked if enough people have to cancel takeoff. I'm thinking if the current or forecast winds are close to 90°, than give us an automatic TW05.

 

I’m terrible at trig

 

In the olden days it was called an E6B. Fit right there in the pocket of your $6.99 E.J. Korvette's summer short sleeve.

 

I’m old enough to own and be plenty familiar with an E6B, but just because I’ve also gone to the opposite side of the globe using paper charts and no FMS doesn’t mean I’m not open to easier methods of completing tasks in the cockpit. I don’t exactly find that dialing the E6B to remotely as easy, day or nighttime, as the one-handed use of the app as PM.

 

5/7/9 rule

at 30degrees off rwy heading, hw=90% of total, xw=50%
at 45degrees off rwy heading, both are 70%
at 60degrees off rwy heading, hw=50%, xw=90%

that simple rule will get you within a knot of nearly every wind scenario you’ll come across.