It's rather simple... the transmission(s) have oil to lubricate the gears, and in the event that the oil is depleted, the gearboxes are designed to run for at least 30 minutes. After which point, the manufacturer cannot guarantee that the gears will not seize.
|Quoting YXD172 (Thread starter):|
2) Are they required for all operations, or is it just a further certification?
Sikorsky gearboxes -- to include the main transmission, the accessory gear boxes, and the tail rotor gear boxes -- are advertised to be rated to a specific "dry run time".
Now... the design intent is to offer a safety window for the pilots, to get on the ground immediately, in the event of a massive oil leak. It is not the design intent to allow for the pilots to feel they can run for an additional 30 minutes and THEN land. The emergency procedure is a "land as soon as possible" - ie: land at the nearest suitable landing area without delay.
I am not criticizing the pilots of this particular crash. I have no idea what went on in that cockpit, and I must defer to their judgment. I have no reason to believe they were to blame for this.
But as a PC
of a Sikorsky helicopter - if I had a low transmission oil pressure, or any associated caution lights - my top priority would be find the nearest spot to land, and quickest route there. I've done numerous over-water missions, and I brief my crew and passengers about water ditching procedures. If I encountered an oil issue, and possibly had to ditch, I would instruct my crew to prepare for a water ditching.
But yeah... even though my manuals tell me I have X amount of minutes before the sh*t hits the fan, I've always preferred to not trust it, and always expect that helicopter is trying to kill me.
Your men have to follow your orders. They don't have to go to your funeral.