 It was discovered that large and sudden temperature changes (e.g., from being parked in the sun prior to becoming airborne) were falsely causing the engine stator blades to close and choke the compressor.The dangers presented by these engine failures were compounded by the downward ejection seat, which gave the pilot little chance of a safe exit at low level.The engine systems were subsequently modified and the ejection seat changed to the more conventional upward type.