NOTAM D item spanning across midnight with EXC

Question

The specification of NOTAM is somewhat flaky. Edge cases may even be hard to parse programmatically unless EUROCONTROL guidelines are being followed as well.

For the sake of simplicity, let's assume the following examples are valid from 2022-01-01 thru 2022-01-31.

D items (which specify the exact validity periods of the NOTAM) may span across midnight as follows:

D) 01-10 2100-0600

This is to be interpreted as follows:

Valid for ten nights beginning with 2022-01-01 21:00 thru 2022-01-02 06:00 and ending with 2022-01-10 21:00 thru 2022-01-11.

So even though the dates mention only 01-10, January 11 is also included as the times span across midnight. So far, so easy.

Things get hairy once exceptions are added to the mix:

D) 01-10 2100-0600 EXC WED

The only Wednesday in that period is on 2022-01-05. The above can be interpreted in two ways:

1. On exactly 2022-01-05, the times do not apply. So the NOTAM is not valid that Wednesday from midnight to 06:00 and from 21:00 to midnight.
2. The entire period starting 2022-01-05 is excluded. So the NOTAM is not valid that Wednesday from 21:00 thru the following Thursday 06:00.

I tend towards interpretation 2 since the other interpretation produces somewhat fragmented validities and I'm having a hard time imagining a situation where this actually makes sense.

But I can't find any hint about this case in the documentations. Has anybody seen such a case in the wild? Or maybe some more detailed official guide as of how to interpret such cases?

Thanks a lot!

Answer 1

I'm a former Brazilian NOF (NOTAM Office) operator. The Brazilian regulation for NOTAM is ICA 53-1 (click on Download do arquivo, open the downloaded PDF file and then see Exemplo 9 at page 42/60), which is compliant with ICAO's DOC 8126 (Chapter 6 - NOTAM) guidelines.

Based on DOC 8126 (Chapter 6) + ICA 53-1 + my experience as NOF operator, on the context described above, if I want to communicate circumstance #1 (i.e. the NOTAM is valid except on Wednesday 00:00 until 06:00 and 21:00 until 23:59), then I must type item D this way:

D) 01-10 2100-0600 EXC WED

(because EXC WED is a short for EXC WED 0000-2359, i.e. it's the whole Wednesday)

...or, alternatively:

D) 01-10 (EXC WED) 2100-0600

...even though the most appropriate way to express it more clearly (it's the one that I would use) is this:

D) 01-03 07-10 2100-0600 04 2100-2359 06 0000-0600 2100-0600

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On the other hand, if I want to communicate circumstance #2 (i.e. the NOTAM is valid from Tuesday 21:00 until Wednesday 06:00 but not from Wednesday 21:00 until Thursday 06:00), then I must type item D this way:

D) 01-10 2100-0600 EXC WED/THU

...or, alternatively:

D) 01-10 (EXC WED/THU) 2100-0600

...even though the most appropriate way to express it more clearly (it's the one that I would use) is this:

D) 01-04 06-10 2100-0600

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If I want the NOTAM to be valid except from Tuesday 21:00 until Thursday 06:00, then the item D becomes this:

D) 01-10 2100-0600 EXC TUE 2100 TIL THU 0600

...even though the most appropriate way to express it more clearly (it's the one that I would use) is this:

D) 01-03 06-10 2100-0600

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In a nutshell:

• WED means the whole Wednesday, while WED/THU means "from Wednesday to Thursday"; and
• NOTAM operators are expected to use number notation instead of abbreviated week day names, precisely because of the confusion caused by these abbreviated names. Usage of abbreviated week day names is only justified when longer periods make number notation impracticable, e.g. 01-14 2100-0600 EXC WED is preferable because number notation would require the text 01-03 07-10 14-15 2100-0600 04 11 2100-2359 06 13 0000-0600 2100-0600 even though the general rule of thumb is that NOTAMs must be short (but also clear i.e. easy to understand: they can't be dubious).