Read the whole MEL line: one landing light out usually doesn't ground you at night
A crew calls in: the left landing light is out. Within minutes someone has read the MEL item, seen the words "not operated between sunset and sunrise," and flagged the aircraft as day-only. Tonight's trip is suddenly in doubt.
In most cases it doesn't need to be. The restriction is real, but it only applies in a situation this aircraft isn't in.
Start with the definitions
Every MEL begins with definitions in its preamble, and Part 135 operators often repeat them in the GMM or MEL procedures. Three columns matter:
- Number installed: how many of the item are on the aircraft.
- Number required for dispatch: the minimum that must work for the aircraft to be legal.
- Remarks or exceptions: the conditions and limitations that apply when you defer the item.
A restriction in the remarks applies when its conditions are met, and not otherwise.
Read the specific line
A typical landing light item on a light or midsize jet reads something like this: two installed, one required for dispatch, Repair Category B. The remarks allow one to be inoperative, and include a provision that the aircraft is not operated between sunset and sunrise.
The key is how those two parts fit together. The night restriction is tied to the aircraft not meeting the number required for dispatch. With one of two landing lights still working, the aircraft meets the dispatch requirement, so the night restriction isn't triggered.
Always read your own MEL. Item numbers, installed counts and remarks vary by aircraft and by operator. The example here shows how to read the line, not what your line says.
Why the misread happens
Under time pressure, people react to key words. "Landing light" plus "sunset" reads like "no night flying," and a cautious restriction feels safe. But an unnecessary restriction isn't free: it cancels trips, frustrates owners and crews, and teaches everyone that MEL calls change depending on who reads them.
Who owns the call
Other departments can and should raise concerns. But interpreting and applying the MEL belongs to Maintenance Control, and restrictions shouldn't be added on assumption or on outside advice. Consistency is the point: the same item, deferred on the same aircraft, should get the same call no matter who is on the desk.
Five habits: start with the definitions; read the entire line, not just the title; apply a restriction only when the conditions require it; document your reasoning in the deferral; and own the decision.
General guidance for orientation only. Your MEL, approved manuals and the regulations govern; confirm against them before acting.