OPS topics

Flying Safety,  Dec, 2004  

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Editor's Note: The following accounts are from actual mishaps. They have been screened to prevent the release of privileged information.

Here are a few events that caused some missed sorties and aircraft damage. Think before you act, and maybe we can prevent things like this from happening.

T-38 Convertible

The student pilot (SP) briefed and stepped for a solo contact training sortie. Following engine start, the SP lowered the front canopy to confirm the canopy warning light extinguished indicating both canopies were properly closed and locked. The canopy warning light went out and the SP opened the front canopy without first selecting ram dump as required by the checklist. Taxi to the end of the runway, including taxing down a parallel runway, was uneventful with a maximum-recorded airspeed of 37 KCAS. The taxi speed did not exceed the Dash 1 published canopy limit of 50 KIAS. When cleared for takeoff, the SP taxied into position, closed the canopy, ran up the engines and initiated the takeoff roll. At approximately 80 KIAS and 300 feet from the runway threshold, the SP heard a loud noise and noted the wind rush as the front canopy departed the aircraft. The SP initiated an abort reaching a peak of 87 KCAS as recorded by the flight data recorder.

Post-mishap aircraft inspection revealed that the front canopy had become unlocked during the takeoff roll and separated from the aircraft when exposed to the relative wind. The front canopy hinges were fully intact with no apparent damage, indicating the release system had functioned as designed. Egress specialists fully demonstrated normal and emergency operation of the canopy movement and locking mechanisms without a canopy installed. Egress specialists also checked operation of the canopy warning lights and activation switches and found they were within specified tolerances. The canopy warning light switch also activates a solenoid in the cabin pressure regulator to begin cabin pressurization and canopy seal inflation when the canopy warning light is extinguished. Therefore, cabin pressurization and canopy seal inflation do not occur until after the canopy is fully down and locked. Maintenance performed a full check of the cabin pressure regulator, and no failures of the regulator were found.

Prior to taxi from the chocks, the SP closed and locked the canopy and checked that the canopy warning light went out. This is a normal practice for a solo pilot to confirm the security of the rear cockpit. Normally, the check is done prior to engine start, but it can be performed after the engines are running. However, if the canopy is lowered with the engines running, the cabin pressure switch should be moved to "ram dump" prior to opening the canopy IAW tech data. Selecting ram dump depressurizes both cockpits and deflates the canopy seals.

Tech data states: "If canopies are opened from the closed and locked position: Cabin pressure switch--ram dump." The checklist further adds the following warning: "Loss of canopy and severe injury may occur if either canopy is unlocked prior to depressurizing to field elevation. The canopy could blow off its hinges and fall into the cockpit area. Anytime the aircraft has been pressurized, ram dump must be selected and the cabin pressure checked prior to opening the canopy." The checklist further adds the following caution: "After placing the cabin pressure switch to ram dump, ensure the cabin altimeter displays field elevation before opening the canopy. Pressure equalization may take several seconds."

There was inadequate evidence to conclusively determine the cause of the canopy becoming unlocked, but the most likely scenario is that the canopy was not fully locked prior to initiating the takeoff roll. Do you know all the procedures to ensure your aircraft doesn't become a convertible?

Emergency Jettison, Oops, No Emergency

The night prior to the sortie, maintenance performed a 30-day weapons inspection on the aircraft. Prior to step, the pilot was notified that the aircraft and another aircraft in the line-up would require an operational check flight (OCF) for extended downtime in conjunction with the mission. The aircraft had not flown in the previous seven days. The Squadron Top 3 directed the pilot lead the two aircraft requiring an OCF on an alternate mission. During ground ops, the pilot discovered that he could not access the armament display of the programmable armament control set (PACS) on the multipurpose color display (MPCD) and called for maintenance. While troubleshooting the PACS, the pilot determined the push button associated with the armament display was not faulty as it could be used to access other MPCD pages. Neither the pilot nor maintenance could correct the display problem. After discussing the amount of time required to replace the MPCD, inoperable systems, and mission requirements with maintenance supervision and the Squadron Top 3, the pilot elected to take the aircraft and continue the mission, and work the PACS problem after landing.