Mountain wave go or no-go

Crossing a mountain wave (AIR 2.10; AWH 19.2.3.2.1):

• Fly at turbulence-penetration speed.
• Avoid flying over terrain that drops away abruptly, even without lenticular clouds.

Pre-flight (RAC 11.7.12): check for MWA or severe turbulence chance:

• Forecast Winds and Temperatures Aloft (FD)
• Area Forecast (FA)
• SIGMETs
• PIREPs

Go/no-go rule of thumb (forecast wind at peak or ridge-top level; ASL 3/2025):

Low-level mountain flying (AWH 19.2.5.3):

• Wind perpendicular to ridge: substantially stronger surface winds, likelier turbulence.
• Downdrafts over forested areas may be strong enough to force aircraft into the trees, even at best rate-of-climb speed.
• High density altitude worsens this.

Trap: using the 50 kt wave-formation figure as the go/no-go limit. Cancel line is 25 kt at peak or ridge-top level.

Practice