I'm not an expert on the heavy iron, so I'll leave it to our resident airline pilots.
However, on the PA28R and PA44 general aviation airplanes (which I have plenty of experience in), the landing gear unsafe light illuminates and the horn sounds under the following conditions:
- The flaps are set past 10 degrees with the landing gear down limit switches not engaged (gear not down)
- The power is reduced past approximately 14" MP
with the landing gear down limit switches not engaged (gear not down)
- The landing gear selector is in the "UP" position with the airplane on the ground (squat switch engaged)
Some of the older Arrows (I've flown one) were produced with an automatic gear extension system that automatically drops the gear when the airplane slows below a certain airspeed. Sounds like a swell idea, but many planes had it removed for several reasons. First, no one really knew exactly
what this magic airspeed was for any given aircraft, the system that sensed the airspeed (it looks like a second pitot/static mast with a garden hose attached to it in the cabin) was darn near impossible to calibrate, and often the gear would free-fall when you definitely didn't want it extended (like during an engine failure...the plane glided like an anvil and the gear didn't help matters). For this reason, in the event of an engine failure at altitude the first thing I was trained to do was lock the gear up with the override until I was certain I would make the intended landing field. Big pain in the rear if you ask me.
[Edited 2011-02-22 22:41:31]
B-52s don't take off. They scare the ground away.