Flight levels


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Flight levels

People living near airports often complain about "aircraft flying too low". But, what most people don’t realise is that it is almost impossible to estimate an aircraft's altitude from the ground. This is due to the way human perception works. The human eye uses, among other things, reference objects to estimate distances – such as a person or a house. While this works quite well looking at things on the ground, when looking at objects in the sky, there are no such reference parameters. Without additional information it is virtually impossible to estimate the actual altitude of an aircraft with the bare eye.

As a rule, air traffic departs following defined procedures. These can, but need not include altitude instructions. Up to a certain altitude, compliance with determined departure routes is compulsory for DFS controllers to keep things safe. Therefore, controllers do not deviate from these routes unless it cannot be avoided, for example in case of a thunderstorm or in extraordinary circumstances. If the pilot makes an early turn or leaves the departure corridor without the controller's permission, he commits an administrative offence.

Minor deviations from the ideal departure route cannot be avoided to a certain extent, e.g. due to the weather or aircraft performance. Therefore, a maximum permitted deviation from the ideal path is determined according to international ICAO standards. Each aircraft must stay within with these tolerance areas. If a mistake can be attributed to a cockpit crew, the Federal Office of Civil Aviation (Luftfahrt-Bundesamt LBA) initiates legal proceedings against the pilot-in-command.

The so-called enroute clearance comprises the initial climb altitude given in the route description, usually 4,000 or 5,000 ft above mean sea level. During this initial climb phase, the controller allocates further altitudes to the cockpit crew depending on the traffic situation. Generally, pilots want to reach a high level as quickly as possible because:

Safety aspects in case of technical problems
Higher speeds
Lower fuel consumption

When the altitude assigned by the controller is actually reached depends mainly on the prevailing meteorological and aircraft conditions. There is no such thing as "minimum flight level" in aviation. Two articles in the German Aviation Regulation (Luftverkehrsordnung) define the term "minimum safe altitude" for flights following instrument flight rules. Article 36 of the German Aviation Regulation applies here: Except for take-off and landing, the minimum safe altitude for IFR flights is defined as at least 300 m (1000 ft) above the highest obstacle located within 8 km of the aircraft. The routes must be defined in such way that the minimum safe altitude can be adhered to when an aircraft deviates within permissible limits from the route (tolerance area, corridors).


07/06/2011	PRINT