Extended Range Twin Engine Operations - ETOPS Diversion
The presence of diversion alternates makes flying ETOPS possible. These alternates allow an operator to execute an ETOPS flight in an area of operation marked by time circles. When making a flight plan, adequate and suitable alternate aerodromes must be determined. Alternate aerodromes are noted in the flight plan and serve as escapes when unexpected system failures occur.

Diversion Strategies
ETOPS demands more strict requirements to determine an alternate aerodrome. There is a difference in alternate aerodrome determination. Adequate aerodromes and suitable aerodromes are both used for the same objective although usage of one another depends on specific minima and aeronautical decision making.

Adequate Alternate Aerodrome
An adequate alternate aerodrome is an aerodrome which is expected to be available, if required. This means landing performance requirements on an adequate aerodrome are required to be met and the concerning aerodrome must have the necessary facilities and services such as ATC, airport lighting, communications, meteorological services, navigation aids, rescue and fire-fighting services and one suitable instrument approach procedure.

Suitable Alternate Aerodrome
In ETOPS, the alternate aerodromes must comply with more strict requirements. An ETOPS aircraft may operate in an environment where few diversion aerodromes are available. Therefore it is important to know whether the alternate aerodromes available are well equipped with the necessary facilities. As stated above, such an aerodrome is called “adequate”. Whether an “adequate” alternate is a “suitable” alternate is decided prior to departure. This decision is based on the weather conditions forecast for the adequate alternate at the Estimated Time of Arrival (ETA). An enroute adequate aerodrome is declared suitable when:

  • Weather forecast of the concerning aerodrome is equal or better than the ETOPS required weather minima for a defined period of time;
  • Applicable NOTAMs ensure the required enroute alternate aerodrome is and will remain available for the same period of time;
  • Surface crosswind forecasts and runway conditions are within acceptable limits to allow a safe approach and landing with one engine inoperative.

Weather Minima
The weather minima are set up by the national authorities of each country. Available facilities are compared with the alternate airfield ceiling and Runway Visual Range (RVR). If more usable precision approach facilities are present serving separate runways, the ceiling and visibility are allowed to be lower. These planning minima are included in the operations manual and can be used for ETOPS planning.

The following table is an example (ETOPS Exposition Manual) of weather minima with one operational navigation facility which must also be included in the Aircraft Operations Manual. For every type of approach the minimum ceiling and visibility are given.

Table 1: ETOPS weather minima
Available at Enroute Airport Ceiling Minimum Visibility Minimum
One runway with at least one instrument approach procedure
Prescribed HAT/HAA + 400 Feet
Prescribed VIS + 1.500 meters
Two separate runways (or more) with at least two separate instrument approach procedures
The higher of the two Prescribed HAT/HAA + 200 Feet
The higher of the two Prescribed VIS + 800 meters

Alternate Aerodromes
When executing a flight it is necessary to find suitable alternate aerodromes. An alternate near the departure aerodrome is called take-off alternate. When operating in flight, enroute alternate(s) can be used if the destination aerodrome is not available.

Take-off Alternate
A take-off alternate is required when the departure aerodrome is not available to return for either meteorological or performance reasons. This means, when the departure aerodrome is not available for return, and no other suitable aerodromes are in the area of operation, the flight can not be executed. Take-off alternates should be in the range of 60 minutes flight time from the departure aerodrome. The weather conditions forecast for a take-off alternate must be valid at least one hour before and after ETA at that aerodrome.

Enroute Alternate
The availability of enroute alternates along the route is important for safe flight execution. When two or more alternates are available these are called operational alternates. In case of diversion due to system failure the Pilot in Command (PiC) is able to choose an operational alternate instead of the nearest alternate. The PiC shall take into consideration which aerodromes are convenient for the company. An operator may prefer an alternate which is one of its hubs or destinations where adequate support to the crew and passengers can be provided. The operational alternate may also be equipped with the necessary facilities which are not available on the nearest alternate aerodrome.

Destination Alternate
When unable to land at the destination aerodrome, because of weather conditions or operational problems, a diversion to a selected destination alternate should be executed. All Instrument Flight Rules (IFR) flights have at least one selected destination alternate. If the destination alternate is provided with two separate runways and the flight time is six hours or less, a destination alternate is not necessary. If the previous is obtained, appropriate weather forecasts must also indicate weather conditions will be at or above applicable planning minima between one hour before and after ETA at that aerodrome. Two destination alternates should be selected when no meteorological information is available or when weather reports or forecasts indicating a period commencing one hour before and ending one hour after the ETA, the weather conditions will be below the applicable planning minima.

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