B737-400
Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine
Communication Breakdown
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural FAR; Deviation / Discrepancy - Procedural MEL / CDL; Deviation / Discrepancy - Procedural Published Material / Policy
General Flight Cancelled / Delayed; General Maintenance Action
Logbook Entry; MEL; Procedure; Human Factors; Aircraft; Company Policy
Pilot in Command (PIC) and I as Second in Command (SIC) conducted 4 flights in Aircraft X. There was a Non-Essential Equipment Furnishing in the aircraft maintenance logbook listed as 25-XXX; Forward Lav flight attendant call button inop; dated [date]. However as my PIC discovered after the flights were completed; this MEL was not the correct one for the aircraft condition.We were again assigned Aircraft X in ZZZ and my Captain was conducting his preflight inspection. He was reviewing MELs and maintenance records and it suddenly stuck us that the attendant call button might not be possible to defer. He reviewed the Minimum Equipment List and noted that MEL 25-XXXX applied to 'Cabin reading lights; light lens covers; and lav occupied lights may be inoperative provided enough light is available for safe working conditions during night operation'. Consequently the MEL did not apply to the flight attendant call button in the forward lav. My PIC checked the expiration date of the Non-Essential Equipment Furnishing; noted that it was still within limits before expiration and he did not investigate further. Consequently; we conducted the flights listed above.My Captain contacted the local Company maintenance personnel and Company Maintenance Control and informed them of the situation; stating that we would not be able to fly the airplane until the issue was corrected and we can legally fly the airplane. Subsequently; the forward lav was locked out and deferred in accordance with MEL 38-XX; paperwork was completed and my Captain conducted all the following scheduled flights for the day; although [flight] was delayed due to the maintenance issue.This has been a recurring issue with incorrect MEL/Non-Essential Equipment Furnishing guidance from Maintenance Control which resulted in aircraft flying when they are legally required to be repaired; grounded; or a more restrictive action is due to be applied.
B737 First Officer reported that an aircraft flew several times with an incorrectly applied MEL.