The bold red numbers on the ICAO chart represent the Maximum Elevation Figure. What do they mean?
Maximum Elevation Figure can be translated as "highest elevation value". There are two calculation methods for determining this value: elevation point evaluation and obstacle evaluation.
Elevation point evaluation
The landscape elevation (elevation point) related to the mean sea level is used. In our example, the elevation of the landscape is 2331 ft AMSL.
A fictitious obstacle of 328 ft (100 m) height above ground is placed on this elevation point. The reason for this fictitious value is that obstacles up to 100 m are not entered in the ICAO chart.
Then a safety margin of 30 ft is added for possible changes in air pressure and setting errors on the altimeter.
The sum of these three values is rounded up to the nearest 100 ft value.
2331 ft + 328 ft + 30 ft = 2689 ft
Rounded up: 2700 ft AMSL
Obstacle evaluation
The height of a known obstacle that protrudes prominently from the landscape is used. In our example, the obstacle height is 2463 ft AMSL.
A safety margin of 60 ft is added to this for any changes in air pressure and setting errors on the altimeter.
The sum of these two values is rounded up to the nearest 100 ft value.
2463 ft + 60 ft = 2523 ft
Rounded up: 2600 ft AMSL
Note: Note: By the way, for the indication on the ICAO chart Germany and the V500 charts the higher of the calculated values is used. An explanation including the calculation methods can be found on the back of the charts.
There is the following question in the PPL questionnaire:
For an obstacle with the altitude of 2850 ft AMSL, which Maximum Elevation Figure would result? Using the obstacle evaluation calculation method, the result can be calculated as follows:
Obstacle height 2850 ft AMSL + surcharge 60 ft = 2910 ft AMSL
Rounded up: 3000 ft AMSL
What is the practical significance of the Maximum Elevation Figure for the pilot?
First things first: the Maximum Elevation Figure is not the same as the minimum safety altitude. But it helps pilots in planning their flight routes and especially in situations where it is necessary to deviate from the planned flight corridor.
When planning a flight, the minimum safety altitude must be taken into account. The MEF assists in determining this.
When a MEF of 13 is given, there is no natural or man-made obstacle higher than 1,300 ft in this 30 x 30 minute rectangle, calculated on the meridian and parallel. This value has been rounded up to the nearest hundred.
Laut SERA.5005 Buchstabe f (im deutschen Luftrecht umgesetzt in §37 der LuftVO) muss eine Mindesthöhe von 500 ft (150 m) über dem Boden oder Wasser oder 500 ft über dem höchsten Hindernis in einem Umkreis von 150 m um das Luftfahrzeug eingehalten werden. Über According to SERA.5005 letter f (implemented in German air law in §37 of the LuftVO), a minimum altitude of 500 ft (150 m) above the ground or water or 500 ft above the highest obstacle within 150 m of the aircraft must be maintained. Over cities, other densely populated areas and outdoor crowds, it is even 1000 ft above the highest obstacle within 600 m of the aircraft. These altitudes may only be undershot during takeoff and landing. Gliders, hang gliders and paragliders, for which it is necessary due to their design, are allowed to fly below the minimum altitude. This can also be read in the Aeronautical Information Publication AIP VFR in chapter ENR 1-16.
If you now add the MEF with the safety minimum altitude, you get a safe flight altitude. Of course, the airspace structure must still be taken into account. But especially in unexpected deviations of a planned flight route, the value is a very helpful indication for a continued safe flight.
The display of the MEF can only be found on the ICAO chart and the European charts of DFS. Charts of other manufacturers show directly the safety altitude. There, the highest point plus a safety distance of 1,000 or 2,000 ft is directly indicated.