LOWER ALTITUDE IN SEVERE TURBULENCE
 

In the old (1990) B737 Training Manual there was a recommendation to descend 4000ft below optimum altitude in case of severe turbulence.

Now the 4000ft figure has been removed, it only says to descend to a lower altitude.

My questions:
1) do you know why?
2) Is it the same on other Boeing models? What's the recommendation on Airbusses?

Thank you
LEM

Might be something as simple as the widespread implementation of RVSM - a 2000ft descent is now an option from any altitude a 73 would be cruising at.

The 4000ft recommendation remains in our 744 manuals.

A lower altitude will provide a wider margin between low-speed stall buffet and high-speed mach buffet, and a higher load factor available before stall. At optimum altitude the load factor at stall buffet is only 1.3 or 1.4 Gs (depending on the operator; we use 1.3).

At 4000' below optimum altitude, maneuvering G available increases from 1.3 to around 1.6 (varies somewhat with weight), according to our performance charts.

As Intruder mentions, a more or less standard procedure for jet transport aircraft, and has been thus for many many years.
In earlier days, 'ole 707 and DC8 pilots learned the hard way, so the younger guys today can benefit from these long ago incidents which, on occasion, turned out rather nasty.

Thaks for your inputs, Gents.

Just to clarify, I'm not asking why it's a good idea to descend in severe turbulence, but rather why they changed the 4000ft figure to a mere "lower altitude" on the 737, and if this 4000ft figure still remains in other types manuals, and what is the exact figure, if any, on the Bus.
:8

Maybe because some eagle-eyed legal eagle at Boeing saw a potentially dangerous legal loop-hole where someone could sue Boeing over the difference between an absolute figure like 4000 ft and the less pedantic and nice vague term "lower altitude.".