How many miles before the runway should an airliner put the gear down? I was watching this video of a FedEx MD-10 landing and some questions came up, of course again the unprofessional YouTube comments didn't help.


How many miles before the runway should an airliner put the gear down?
Was the aircraft in the video too close?
At which distance does radio altimeter warn the pilots?
Is the following YouTube comment accurate?



  This was FedEx flight 1356 and I can tell you what happened. During approach there was an anomaly on the left slat and it was being watched. Also during approach engine no.1 was heating up to unacceptable levels and because of all of this the gear wasn't lowered right away. It was only due to TCAS and the alarms on board that it was noticed as the aircraft was approaching it's minimums. Upon landing the crew was reprimanded for not following proper procedure and was suspended with pay.
To answer the last part of your question, as ratchet freak said, the TCAS doesn't warn the pilot when he should deploy landing gear. However, the ground proximity warning system/terrain avoidance and warning system (GPWS/TAWS) does. GPWS Mode 4A is "Unsafe Terrain Clearance With Landing Gear Not Down". 

If the plane is less than 700ft (based on the radio altimeter's measure) high and under mach .35, there is an aural alert in the cockpit saying "Too low - gear". The message is repeated until the situation is corrected.

So the warning is based on the height and speed of the aircraft. Not on its distance to the airport.