If you started with a full-up superhet, dual-conversion AM receiver, then your task is simple. Such receivers have an Automatic Gain Control, which detects the "average" signal level at the AM detector, amplifies it, and applies it as a gain-reducing control voltage to the RF amplifier, and first IF gain stages. The voltage on the AGC line in such a receiver is proportional to the signal level at the antenna terminals. In some receivers, the AGC line is connected to the S-Meter, if there is one...
For your purpose, simply sampling the AGC line from the receiver using a PIC's A/D converter would give you both the signal level, and the timing of any pulses sent by keying the aircraft's transmitter.
A suitable receiver would be a retired aircraft COM receiver, or a
kit like this one, or put a 120MHz to 27MHz RF converter ahead of an old CB the receiver of which is use as the IF/detector..
btw, my aircraft are based at an airport that has Pilot Controlled Lighting.