Narrative:

When we arrived at our aircraft; MEL 33-1B was in the logbook. We reviewed the MEL & associated procedures and thought ok; so the backlighting may be quite dim once it is nighttime; however the frequency lights are clearly illuminated now (late afternoon & bright outside) so they will continue to work later & this should not pose too much difficulty. However; what we discovered as the sun went down was the frequency lights weren't just dim; they were literally impossible to see. There was also no lighting for any of the buttons on either FMC keypad. We had to shine a flashlight on the pedestal and FMC to tune new frequencies and route changes. My pilot monitoring worked hard as he was trying to use the grimes sidewall light as dimly & carefully as possible to protect my night vision; (this was our best option as our regular flashlights were so much brighter). What made this more challenging was it occurred during the approach and landing phases of flight when we had our highest workload...I was unable to back him up even though I was using automation as long as possible because I couldn't see the necessary buttons to tune the radios or program the FMC.this MEL states that 'individual lights may be inoperative provided: remaining lights are sufficient to clearly illuminate all required instruments; controls; and other devices for which they are provided.' unfortunately; what we discovered once it got dark outside; is the all of our panel lighting was now inoperative so without the flight deck main overhead light on; or use of a flashlight; we could not see the numbers on the radio panel to change frequencies or type changes or even navigate through the FMC. In our situation; with none of the panel lighting being operative - this MEL should have been daytime only. Perhaps there are other failures where only some of the lighting capability is lost; but in our scenario we agreed the workload became too high at a critical time of flight to be safely operated at night.

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Original NASA ASRS Text

Title: B737-900 First Officer reported accepting an aircraft with a cockpit lighting MEL 33-18. After the sun went down it was discovered the lighting is inadequate and greatly increased the workload.

Narrative: When we arrived at our aircraft; MEL 33-1B was in the logbook. We reviewed the MEL & associated procedures and thought ok; so the backlighting may be quite dim once it is nighttime; however the frequency lights are clearly illuminated now (late afternoon & bright outside) so they will continue to work later & this should not pose too much difficulty. However; what we discovered as the sun went down was the frequency lights weren't just dim; they were literally impossible to see. There was also no lighting for any of the buttons on either FMC keypad. We had to shine a flashlight on the pedestal and FMC to tune new frequencies and route changes. My pilot monitoring worked hard as he was trying to use the Grimes sidewall light as dimly & carefully as possible to protect my night vision; (this was our best option as our regular flashlights were so much brighter). What made this more challenging was it occurred during the approach and landing phases of flight when we had our highest workload...I was unable to back him up even though I was using automation as long as possible because I couldn't see the necessary buttons to tune the radios or program the FMC.This MEL states that 'individual lights may be inoperative provided: Remaining lights are sufficient to clearly illuminate all required instruments; controls; and other devices for which they are provided.' Unfortunately; what we discovered once it got dark outside; is the ALL of our panel lighting was now inoperative so without the flight deck main overhead light on; or use of a flashlight; we could not see the numbers on the radio panel to change frequencies or type changes or even navigate through the FMC. In our situation; with NONE of the panel lighting being operative - this MEL should have been daytime only. Perhaps there are other failures where only some of the lighting capability is lost; but in our scenario we agreed the workload became too high at a critical time of flight to be safely operated at night.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.