Hawker Driver

It was very interesting, eye opening and kinda scary to experience one of the strongest mountain wave phenomena of my career at FL 400 yesterday. It extended about 200 miles and was east of Phoenix. Mach speed variances up to +,- .04!

We were adjusting the throttles so much that my colleague quipped something about wishing we had auto throttles. We both decided to try and go higher to get over it.......

Soon after, while climbing at .7 Mach, the bottom dropped out from under us.-- .67, .65, .62!(178knots) in a span of some 10 seconds. The red tape indicating our stall speed was just 20+ odd knots lower.

During the encounter, I recalled an accident years ago where a Westwind had crashed after entering a mountain wave. I could never understand or even conceive how such a thing could have occurred until now.

Be careful out there!

HD

UnderOveur

Looks like the jetstream has pushed a little further south today. Wicked.

GeelErmo

Just keep it easy! Set N1 at cruise settings! Like 93% on our (Falcon50) it gives us .76 at FL 350 And dont worry about gains/loses of ur speed! Less u play with the throttle, safer u r!:-) good luck!

JohnBurke

I've found that in strong wave activity, disconnecting the autothrottles and manually setting power (without moving it much) works much better.

Hawker Driver

Thanks for the kind suggestions guys!

Blackwing

What about asking for a block altitude and riding it out?

Hawker Driver

I like that suggestion. Since altitude was never in question, it never occurred to me.

221340

The worst mountain wave I ever experienced was in the NWern US at FL410 in a B757. Entering the positive performance side of the wave, the AP pitched down in an attempt to maintain altitude. Then the autothrottles actually came all the way to idle in an attempt to prevent an overspeed. At that point, at barberpole and idle power, the plane started climbing! I was able to stop the climb with very slight speedbrake application and was able to get a clearance to a lower altitude because the other side of the wave would be next and there was no way we would have sufficient thrust to hold altitude and airspeed. Wild ride that day.