Question about maximum elevation figures

[CharlieDeltaUK]

Just doing some nav planning. Looking at the MEF in each section of the chart, I'm looking to see where in that section is the ground which is likely to feature the MEF. In many instances, the MEF is higher than the spot heights or other elevations. Why would that be?

[BEagle]

If you look at the bottom left hand corner of the CAA half-mill chart, you will find the explanation.....

[CharlieDeltaUK]

I did that before posting my question. Are you referring to the "allowing for unknown features" note?

[BEagle]

Correct. An obstacle of less than 300ft a.g.l. (e.g. a temporary mast) doesn't have to be notified to the CAA - so the MEF allows for this. For example, Lundy Island has a spot height of 466ft - but an unknown obstacle of 299ft might exist, so the MEF is (466+299) = 765ft, which is rounded up to the 08 shown on the chart.

[CharlieDeltaUK]

Thanks for your help

[BackPacker]

The other thing to be aware of is that the UK ICAO chart you're using has MEF figures on it. But charts from other providers, in particular Jeppessen, may have MSA figures on them instead. Essentially MSA = MEF plus 1000' but there are some subtle situations where that's not quite the case.