APATC-1 vs PANS OPS vs MIPS safety altitude

[Bouyacasha]

Dear all,

Working in the Linconshire area, we've recently noted that various local terminal charts use differing MSAs, despite being based on the same mast. Cranwell and Coningsby use APATC-1 which has 2700'. Waddington and Barkston Heath use MIPS which has 2600'. Humberside uses PANS OPS(ICAO) which has 2700'.

The only information I've found in the books is that PANS OPS will calculate safety altitude using metres then convert to feet, which may give slight discrepancies when rounded up (Military Manual of Air Traffic Management- page 36).

Is anyone aware of anything else that might be causing the differing values?

Thanks for you help

[seilfly]

Yes, ICAO uses meters (SI length), and converts to feet. But what is strange is that the MIPS-number differs from the PANS-OPS-number above. MIPS is based on PANS-OPS, not TERPS (ie APATC-1).

I know for PANS-OPS, the MSA is based on a 25NM radius + 5 miles outside both the range (30nm), and 5 miles each side of the borders between the Min Sector Alt-sectors...

I would expect MIPS MSA to be similar to (the same as) PANS-OPS! I do not have the MIPS-documentation here, but I will check tomorrow at work IF I remember to do so :)

[Bouyacasha]

Many thanks. No-one at work has managed to get to the bottom of this.... yet! I'll keep my fingers crossed.

[seilfly]

No result, searching for the text MSA in the MIPS supplements for both vol 1 and 2 of PANS-OPS.

Best guess... Are the dates of the plates different? Has the AD elevation changed past a threshold of rounding up? (i.e. from 99 to 101ft)?

We have had elevation figures updated here recently... :)

[Bouyacasha]

The dates are all very similar and the mast is 1552' AGL, so shouldn't be susceptible to 100' rounding errors. Thanks for your efforts. I know it's a trivial point, but it's starting to really bug the OCD part of my brain! I think I'm going to have to contact No1 AIDU who supply our documentation to see if they know why (or if it's a misprint that no one has ever questioned).

If I have any luck, I'll let you know :)

[Bouyacasha]

After all that, it's the heights on some charts that were wrong! I spoke to AIDU today and they are changing all the published heights to 2600'. Thanks for looking into it for me.