I apologize for what seems to be a simple question but I'm looking for the FAA's legal interpretation on this to no luck.

How do you ascertain the "preceding" 90 days if I'm flying tomorrow?

Do you:

a. Start counting back from tomorrow? ie. Tomorrow is day one, today is day 2 until you reach 90 days.

b. Do you start counting from today and going back 90 days. Today being day 1 and tomorrow not being counted.

Please advise and if you have a FAA legal interpretation please link it.

Thanks.

I've always just counted from the last day you did the evolution (landings, hours etc.) since that's the way our trackers were built. The last day you landed is day zero and count forward from that.

Ok, so your understating is that it's option b. In other words, you could be doing your flight on day 91 (outside the 90 day window)?

While there does not seem to be Chief Counsel interpretation, the reg says "within." That would lead me to believe that clock starts the day the landing is logged. Make three landings today and you have 89 days to log three more. If you start counting tomorrow and go 90 days your landings would not be "within" 90 days if you look back.

The issue is the interpretation of "preceding". Twin Wasp, I think our understanding is the same. I would venture to say that the intent of the FAA was for the flight to fall "within" the 90 day window as opposed to within the "previous" as opposed to "preceding" 90 days. Words matter.

NLT on the 90th day.

If the last day you did the landing counted as 0 and count up to 90, that is actually 91 calendar days.

Definition of preceding
: existing, coming, or occurring immediately before in time or place <the preceding day> <preceding paragraphs>

Absent written FAA clarification I would go with last LDG = day one.

Although nobody probably cares either way (unless something bad happens).

Rickair, that is my understanding. Regarding the importance of it, I think that it matters since evidently its ambiguous enough that pilots and operators interpret it differently.