Removal from the aircraft is by a three part pyrotechnic sequence. A gun catapult provides the initial removal of the seat from the aircraft. A rocket sustainer provides zero/zero capability to the seat. To prevent the seat from tumbling when the aircraft is in a roll maneuver or there is a center of gravity imbalance, another (smaller) rocket called a STAPAC is attached to a gyroscope. This senses the motion and attempts to keep the seat from spinning by automaticly providing a correcting force.
Once clear of the aircraft, the pitot - static system on the seat measures the conditions and selects one of three operating modes depending on the conditions present at egress.
Mode 1 - Low speed (<250 knots) and low altitude (<15 000 feet) operation.
The main parachute deploys as the seat clears the rails. Drogue parachute remains undeployed to prevent line tangle.
Mode 2 - Moderate speed (250-650 knots) and low altitude (<15 000 feet) operation.
Drogue parachute deploys as the seat leaves the rails. Main parachute deploys 0.8 to 1.0 seconds after the drogue. Drogue chute is then released to prevent line tangle.
Mode 3 - High speed (250-650 knots) and high altitude (>15 000 feet) operation.
Drogue parachute deploys as the seat leaves the rails. The pitot - static system senses the conditions and delays the main parachute until mode 2 conditions are met. Then the main parachute deploys after 0.8 to 1.0 seconds. Drogue chute is then released to prevent line tangle.