CAT.POL.H.420 Helicopter operations over a hostile environment located outside a congested area

SAFETY RISK ASSESSMENT

(a)Introduction Two cases that are deemed to be acceptable for the alleviation under the conditions of CAT.POL.H.420 for the en-route phase of the flight (operations without an assured safe forced landing capability during take-off and landing phases are subject to a separate approval under CAT.POL.H.400(c)) are flights over mountainous areas and remote areas, both already having been considered by the JAA in comparison to ground transport in the case of remote areas and respectively to multi-engined helicopters in the case of mountain areas.

(1)Remote areas Remote area operation is acceptable when alternative surface transportation does not provide the same level of safety as helicopter transportation. In this case, the operator should demonstrate why the economic circumstances do not justify replacement of single-engined helicopters by multi-engined helicopters.

(2)Mountainous areas Current generation twin-engined helicopters may not be able to meet the performance class 1 or 2 requirements at the operational altitude; consequently, the outcome of an engine failure is the same as a single-engined helicopter. In this case, the operator should justify the use of exposure in the en-route phase.

(b)Other areas of operation For other areas of operations to be considered for the operational approval, a risk assessment should be conducted by the operator that should, at least, consider the following factors:

(1)type of operations and the circumstances of the flight;

(2)area/terrain over which the flight is being conducted;

(3)probability of an engine failure and the consequence of such an event;

(4)safety target;

(5)procedures to maintain the reliability of the engine(s);

(6)installation and utilisation of a usage monitoring system; and

(7)when considered relevant, any available publications on (analysis of) accident or other safety data.

EXAMPLE OF A SAFETY RISK ASSESSMENT

(a)Introduction Where it can be substantiated that helicopter limitations, or other justifiable considerations, preclude the use of appropriate performance, the approval effectively alleviates from compliance with the requirement in CAT.OP.MPA.137, that requires the availability of surfaces that permit a safe forced landing to be executed. Circumstances where an engine failure will result in a catastrophic event are those defined for a hostile environment:

(1)a lack of adequate surfaces to perform a safe landing;

(2)the inability to protect the occupants of the helicopter from the elements; or

(3)a lack of search and rescue services to provide rescue consistent with the expected survival time in such environment.

(b)The elements of the risk assessment The risk assessment process consists of the application of three principles: a safety target; a helicopter reliability assessment; and continuing airworthiness.

(1)The safety target The main element of the risk assessment when exposure was initially introduced by the JAA into JAR-OPS 3 (NPA OPS-8), was the assumption that turbine engines in helicopters would have failure rates of about 1:100 000 per flying hour — which would permit (against the agreed safety target of 5 x 10-8 per event) an exposure of about 9 seconds for twin-engined helicopters and 18 seconds for single-engined helicopters during the take-off or landing event. An engine failure in the en-route phase over a hostile environment will inevitably result in a higher risk (in the order of magnitude of 1 x 10-5 per flying hour) to a catastrophic event. The approval to operate with this high risk of endangering the helicopter occupants should, therefore, only be granted against a comparative risk assessment (i.e. compared to other means of transport, the risk is demonstrated to be lower), or where there is no economic justification to replace single-engined helicopters by multi-engined helicopters.

(2)The reliability assessment The purpose of the reliability assessment is to ensure that the engine reliability remains at or better than 1 x 10-5.

(3)Continuing airworthiness Mitigating procedures consist of a number of elements:

(i)the fulfilment of all manufacturers’ safety modifications;

(ii)a comprehensive reporting system (both failures and usage data); and

(iii)the implementation of a usage monitoring system (UMS). Each of these elements is to ensure that engines, once shown to be sufficiently reliable to meet the safety target, will sustain such reliability (or improve upon it). The monitoring system is felt to be particularly important as it had already been demonstrated that when such systems are in place, it inculcates a more considered approach to operations. In addition, the elimination of ‘hot starts’, prevented by the UMS, itself minimises the incidents of turbine burst failures.

ENDORSEMENT FROM ANOTHER STATE

(a)Application to another State To obtain an endorsement from another State, the operator should submit to that State the safety risk assessment and the reasons and justification that preclude the use of appropriate performance criteria, over those hostile areas outside a congested area over which the operator is planning to conduct operations.

(b)Endorsement from another State Upon receiving the endorsement from another State, the operator should submit it together with the safety risk assessment and the reasons and justification that preclude the use of appropriate performance criteria, to the competent authority issuing the AOC to obtain the approval or extend the existing approval to a new area.