FAA Chart cycle--Why 56 days?

[Domenick]

While downloading the last digital data set (sectionals, TAFs, and supplements) from the FAA:

https://www.faa.gov/air_traffic/flight_info/aeronav/digital_products/

a question occurred to me.

Why 56 days?

It doesn't divide evenly into 365 or 366, so every year the release dates differ. Why not simply start on 01 January and have a 73 day cycle with 5 releases a year and go 74 days on leap years?

Yeah, yeah, I know 56 days is exactly 8 weeks. So what? Why not 10? Or 12? How much can a chart change? And who picked Thursdays?

Inquiring minds want to know.

 

[midlifeflyer]

For others, I'll repeat what I responded in another forum.

I can't tell you the original reason for the 8-week except that it's an international standard that's been around since the 1960s. The change to the Sectionals from 6 months to the standard for the digital world was set to conform to the existing schedule for instrument charts and procedures. Those can and do change substantially from release to release. Here's the start of the list of instrument flight procedures which have either been added, deleted, or changed since the prior 56 day cycle.



Consider that faster updates also means less NOTAM to wade through.

 

[Palmpilot]

As someone who has managed GPS database updates for CAP aircraft, I found the consistency of always having the expiration occur at the same day of the week very helpful.

 

[farmerflier]

So my 2007 chart is out of date is what you are telling me...

 

[2P2]

So my 2007 chart is out of date is what you are telling me...

Not exactly.

It is a little known conspiracy of Calendarists (the secret medieval Guild of Calendar Makers). But there are only a limited number of calendars (and of thier side-hussle, making FAA Sectional Charts).

These items simply repeat on a pattern. So, your 2007 chart was good in 2019, will be good in 2027, and then will repeat being valid in intervals of 11 and 6 years (with the odd 12 and 7 year gap because of leap years being tossed in there).

 

[Domenick]

...The change to the Sectionals from 6 months to the standard for the digital world was set to conform to the existing schedule for instrument charts and procedures. Those can and do change substantially from release to release. Here's the start of the list of instrument flight procedures which have either been added, deleted, or changed since the prior 56 day cycle.

Good to know. I'm just a lowly VFR pilot.

My digital calendar has a 56-day reminder for new release dates. I also wrote a few PowerShell scripts to automatically download the Sectional, TAC, and Supplement sets making it relatively painless.

 

[Aeromot]

56 days is much better than 53 or 59.