When is a good time to extend the landing gear according to FAA rules for landing?
Basically when you feel like it. There's no true regulation on gear, except that it's best to land ON them, and they do tend to work better when they're down. I usually extend them when i'm alligned with the runway on final approach, but still a few miles back.
Don't drop 'em at much over 180kts though
As everyone else said, there is no FAA rule for extending the landing gear. In a faster aircraft such as airliners or corp. jets, many pilots use the landing gear to the help slow down for the approach in which case extending them up to 10 miles out. On an ILS approach most airlines require the aircraft the be configured for landing upon reaching the final approach fix (outer marker) to ensure a stable approach. Plus, most ATC's require an aircraft to maintain at least 180 kts to the marker.
In a piston powered aircraft, I've always dropped the gear at midfield downwind or again at the outer marker on an ILS.
Some turbo charged piston aircraft actually recommend using the landing gear as a speed brake on the descent to avoid reducing power and shock cooling the engine in the low ambient temps.
So to sum it all up...it depends.
I used to work about six miles north of Boston's Logan Airport. All passenger airliners had the landing gear down a few miles before they passed my position for approaches to Rwys 22R or 22L. Not so with the smaller commuter a/c, they would wait longer.
The A340 pilots are required to lower the gear when they are 1200 ft from the ground.
Is that an aircraft specific requirement or airline requirement? It may be a function of the ground proximity warning system, that automatically lowers the gear.
I used to fly a plane that had an auto extension system on it. When the aircraft slowed to 95 knots, under I beleive 14 inches of manifold pressure the gear automatically extended. The problem with this is, if the system wasn't over ridden, and a go around was required, the gear would not retract until above 95 knots which would cause a terrible climb rate until reaching 95 knots. The system did have an overide switch, which was used about 99% of the time.
I think it may be SOP's [Standard Operating Procedures] for Air Mauritius but I'm not all that sure because it's in one of their four manuels that the pilots are provided with.
For IFR, a hair above the glide slope. For VFR, established on downwind leg. These are typical. The exceptions are: POH/AFM, Company policy and specific ATC/airport procedures. 😀