Things to keep in mind before diverting to the
There are many things to take in account before selecting an alternate aerodrome to divert.
First of all we have to select an adequate aerodrome. But … what is an adequate aerodrome ?
Adequate aerodrome is the aerodrome on which and aircraft can be operated, taking account of the applicable performance requirements and runway characteristics, and of course the fuel requirements we need to reach it.
First of all we must check the landing distance available and landing distance required.
Secondly: we must check in which condition is the runway :
A runway is considered contaminated when more than 25% of the surface area is covered by the following:
Thirdly: we must check the operative restrictions . Written in the NOTAMS , status of the plane.
When do we have to select a take off alternate aerodrome different from which we have taken off ?
When it is not possible to return to the aerodrome which we have taken off due to weather conditions or performance ( for example we have enough runway distance for take off but not for landing).
Which aerodrome is suitable as a take off alternate ?
By law it must:
In the event of the failure of the critical engine at any point along the route, the airplane must be able to continue the flight to an aerodrome, which the landing can be performed safety.
Minimum en route altitude ( MEA) : Segment length up to 100 NM = +/- 10 NM of track, with radio navigational aids reception and minimum of :
Minimum sector altitude (MSA): 1000 ft above above terrain and obstructions within the sector distance ( 25 NM) rounded up to 100 ft.
Minimum off-Route altitude (MORA)
Is calculated for an area bounded by every or every second LAT/LONG square on the route facility chart, and is based on a terrain clearance as follows:
It must be an adequate aerodrome ( check above the definition of adequate aerodrome)
For planning reasons at least one destination alternate must be selected in case our destination does not accomplish with this requirements:
Summarizing: by law if our destination does not accomplish with this requirements or you can not have weather information you must select two alternate aerodrome.
When selecting an alternate aerodrome it must be above the minima shown in the table below:
(For checking what a CATII or CAT III mean check our article : low visibility definitions ).