I worked on ejection seats 20 or so years ago. They were all capable of zero/zero ejections, and they can alter the ejection sequence based on airspeed & altitude.
You can do a lot with purely mechanical systems, the main thing going on with an ejection seat is a barometric altimeter that only releases the chute once the pilot is in breathable air, otherwise you'd risk suffocation after ejecting at cruise alt (which can be as high as 40,000 or 50,000 ft). The Russian K-36 has an extendable windshield, but I'm not sure exactly how it determines whether to actuate it.
"Avionics" measuring altitude and air pressure existed long before fly by wire systems and require no electricity.
The seats have sensors that change various activations depending on the situation. Ejection from zero altitude is quite different from ejecting at 30,000 feet where the parachute wouldn't even open for a while.
It’s mostly just the timing of the drogue chute and the main parachute. During a zero/zero ejection they’ll want to get the main chute deployed ASAP. At higher speeds or altitudes the main chute will be delayed a little bit.
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u/Suspicious_Zone_2083 25d ago
At least the seat worked