Max allowable power - PT6
 

Hi,

A clarification, please:

Pratt and Whitney PT6... what does 'max allowable power' mean?

Some colleagues consider it as the maximum continuous or, for 20 seconds, the transient margin. However, other pilots consider move the power levers to the limit (full forward), although reaching "red" values, without any reference about numbers and/or time limitation.

Thanks.

Uhhh..... power levers full forward and values in the red I'd say is probably NOT ok. Unless it's a light naturally aspirated fixed pitch piston or something with a FADEC, you generally have to set power appropriately and NOT just jam the power levers forward!!! Well, some turbocharged airplanes with turbo controllers can also go full forward... Depends on the plane. Point is, with most airplanes, you can't jam the power all the way up. If I just jam the power lever all the way forward on the PT6 powered airplane I usually fly, that would be.....expensive. I find it difficult to understand that professional pilots would operate an aircraft like this, unless it's specifically designed and approved to work like that.

For a PT6, I've always been taught that the limits are the limits and are not normally to be exceeded, with a little buffer zone for temporary transients.... and some variants may have other time limits on certain power settings. Point is, operate it per aircraft manufacturer/engine limits and company procedures. Routinely jamming things full forward into the red seems......terrible? Also, even when it is permissible to fully advance the power levers, it should always be deliberate and with care, especially for mechanically controlled engines....

Call it what you want, but the maximum operating limits are published in the AFM and TCDS. Exceed those and there are usually maintenance requirements. Here's a short P&W article on the topic and a link to the FAA TCDS.