Everyone who closes out flight hours has had this argument: the flight showed 1:09 on the clock. How many tenths is that?
The intuitive answer, 9 ÷ 60 = 0.15, rounds to 1.2, and is wrong. By the ANAC table, 1:09 is 1.1 h. And it is not an isolated case: the "divide by 60 and round" calculation diverges from the official table in 10 of the 60 minutes, those ending in 3, 9, 15, 21, 27, 33, 39, 45, 51 and 57, always upward, always by 0.1 h. In round numbers, one flight in six closes with the tenth of the neighbor above.
It seems like a detail until you multiply: 0.1 h extra in 17% of entries inflates the logbook, advances maintenance due dates calculated by hour, and creates the classic divergence between your tracking and that of the operator who checks against the table taped to the wall.
The official table
The reference is IAC 3252-121/135-0197, and its rule is to cut the band halfway down: each tenth covers six minutes, but shifted relative to mathematical rounding:
| Minutes | Tenths |
|---|---|
| 0:01 – 0:03 | 0.0 |
| 0:04 – 0:09 | 0.1 |
| 0:10 – 0:15 | 0.2 |
| 0:16 – 0:21 | 0.3 |
| 0:22 – 0:27 | 0.4 |
| 0:28 – 0:33 | 0.5 |
| 0:34 – 0:39 | 0.6 |
| 0:40 – 0:45 | 0.7 |
| 0:46 – 0:51 | 0.8 |
| 0:52 – 0:57 | 0.9 |
| 0:58 – 0:60 | 1.0 |
Two points that often slip by:
Minutes 58 and 59 carry. A 1:58 flight is not "1.9 and change." It is 2.0 h. The final band rounds up to the next hour, and controls that do not handle this break exactly at the end of the month, when the long blocks appear.
"Round" minutes deceive. 0:15 looks like 0.25 → 0.3? No: 0:15 is 0.2 by the table. It is the kind of conversion nobody gets wrong with the table in front of them, and almost everyone gets wrong in their head.
Where the divergence gets costly
In the logbook, systematic upward accumulation inflates the declared experience, and the divergence between your total and the operator's becomes a recurring argument.
In maintenance, a component controlled by hour expires by the number entered. Wrong tenths advance (or delay) the due date, and a CTM that does not close against the logbook is a classic source of audit findings.
In billing, schools and operators that charge by flight hour effectively have a rate 0.1 h higher in one sixth of flights, in favor of one side and against the other, always.
How Alis handles this
The platform solves the issue at the root, with two architectural decisions:
- The whole minute is the source. A 1:09 block is stored as 69 minutes, exact. The clock that appears on screen comes from there, never from a reconversion of the decimal, which would return minutes nobody flew.
- The conversion to tenths follows the IAC 3252 table, implemented band by band and tested minute by minute against the rule, including the 10 divergences and the 58/59 carry. 1:09 becomes 1.1 h in the database, in the logbook, in the pilot logbook and in maintenance tracking: the same number everywhere.
That is why the screens show both formats side by side, 1:09 and 1.1 h, without contradiction: one is the clock, the other is the rule. It is what the operator has taped to the wall, now inside the system.
This article is informational. The regulatory reference for the conversion is IAC 3252-121/135-0197; confirm the current version and the rules applicable to your operation in ANAC publications.