B737 flight crew reported non compliance with operational portion of an engine ignition MEL after flight reviews.
Synopsis
B737 flight crew reported non compliance with operational portion of an engine ignition MEL after flight reviews.
Narrative
On our first flight this day from ZZZ to ZZZ1 we had our #1 engine that failed to start with the right ignition system. This was reported to Maintenance Control and we were required to return to the gate for Maintenance. Maintenance Control applied MEL for the right ignition system on the #1 engine. We continued with our flight to ZZZ1 and on to ZZZ2 on the same aircraft. It was reported to me today that this aircraft had been taken out of service later that day and that maintenance had possibly not complied properly with the MEL procedure. It was also brought to our attention that the engine did not start properly in compliance with this procedure when departing ZZZ2 for ZZZ later that day by the next crew (before the aircraft was taken out of service in ZZZ). The First Officer and I discussed our actions and thoroughly reviewed the MEL procedure today when we were made aware of this occurrence. Name; recalling our subsequent discussion and review of the MEL; we realized that we also had not properly complied with the Operational portion of the MEL procedure; and that is the reason for this report. In the initial part of the MEL it is stated that the Ignition Select switch should remain in the both position. However; on the following page under the O - ops placard procedure; step C states to set the ignition switch to R for the associated engine start. We had missed this step having read the earlier statement that the ignition switch be left in the both position. It is stated later in the MEL procedure that the ignition switch should only be positioned to both after engine start. As a result of our mistake we started the engine in the both position on both flight legs incorrectly. Because of this error we had a successful engine start on both legs. Had we followed the procedure correctly we may have discovered that Maintenance incorrectly applied their v procedure as well (with an unsuccessful start which occurred later that day).
Second reporter narrative
First flight of the day number 1 engine failed to start; using the right ignition. Called Maintenance. Returned to the gate and maintenance MEL the right ignition system. Then we proceeded to ZZZ1 and then to ZZZ2. The following day we learned that the aircraft had been taken out of service because the number 1 engine did not start properly. After some discussion between the Captain and I we concluded that possibly we had executed our portion of the MEL procedure incorrectly. We were not sure however due to the confusing way the MEL is written. Specifically step B of the flight crew procedure we found confusing. We had watched maintenance verify the ignition system operation with one tech on the flight deck and one at the engine communicating directly with one another via phone. This may have led us to misinterpret out portion of the MEL. At the time of the event we thought we had executed the procedure correctly.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.