Unserviceable Fuel Gauge, Transponder Deferral and a Due Inspection
At your Part 141 school, a Cessna 172S has a transponder due for its biennial check and a fuel gauge that fluctuates between full and three-quarters. Maintenance signs a deferral for the transponder under the operator's maintenance programme but refuses to defer the fuel gauge because it affects fuel management. The aircraft is booked for a 2.5-hour dual cross-country through Class C airspace. The student has paid and needs the controlled-airspace experience. The maintenance provider says the fuel gauge is 'probably a sender' and can be looked at next week. The aircraft's annual review is current, but its 100-hour inspection is due in 3 flight hours. The chief pilot asks you to take the flight because the student is ready and the weather is good. The aircraft has a current certificate of airworthiness and the defect has been entered in the technical log.
1. Is the aircraft airworthy for the planned flight? Address the fuel gauge, transponder, 100-hour inspection and your authority as PIC and instructor.
Read the worked answer
No. A known unserviceable fuel gauge that maintenance will not defer is a defect affecting airworthiness and fuel management. You cannot treat it as 'monitor' just because the sender is suspected. The transponder deferral may permit flight only subject to the maintenance programme's conditions; it does not automatically authorise Class C operations, and controlled airspace normally requires a serviceable transponder. The 100-hour inspection due in 3 hours is not exceeded by a 2.5-hour flight, but the margin is thin and any delay or holding could exceed it; in any case the fuel gauge is decisive. As PIC you are responsible for pre-flight action and for accepting the aircraft. As instructor you are also responsible for not endorsing a student into an unairworthy aircraft. The flight should be cancelled or the aircraft swapped.
2. What defect and maintenance records must be made, and what should you tell the chief pilot and student?
Read the worked answer
Enter the fuel gauge defect in the technical log with date, description and the fact that it is not deferred. Ensure maintenance certifies any deferral or rectification properly, and record the transponder deferral reference and any operational limits. The organisation should record the cancellation and rebooking. Tell the chief pilot that the aircraft is unavailable and why, in writing if necessary. Tell the student honestly that the aircraft is not airworthy for the flight and rebook; do not imply that the school is simply disorganised. Do not pressure maintenance to sign a deferral without approved data. If the aircraft is later ferried to maintenance, that requires a proper ferry/positioning authorisation under the maintenance programme, not a normal training flight with a student on board.
3. Could you fly the aircraft outside controlled airspace to the maintenance base? Explain.
Read the worked answer
Only if the maintenance programme and CAA rules permit a ferry flight with the defect, and you have the required authorisation. A ferry flight is not a training flight; it must be minimised and conducted under any conditions in the approval. If the fuel gauge is not deferrable and affects fuel quantity indication, even a ferry may be unsafe unless fuel is dip-checked and the route is short and pre-planned. You cannot carry the student for 'experience' on a ferry flight. The decision rests with the operator, maintenance and PIC, not with the chief pilot's schedule. If there is doubt about the ferry approval, do not fly; obtain a maintenance inspection or transport the aircraft by other means.