OPERATIONAL APPROVAL FOR HELICOPTER FLIGHT IN LIMITED ICING CONDITIONS

1. OPERATIONAL APPROVALFORHELICOPTER FLIGHT IN LIMITED ICING CONDITIONS COMMENTS ON THE HSST DRAFT NPA PROPOSALS OST 05/02

2. The CJAA Operations Division accepts the basic concepts outlined in: • The HSST Draft NPA Proposal, • and • The JAR 29 Special Condition. • However • given the declaration in the Special Condition that the Supplement for Flight in Icing Conditions in the Flight Manual does not constitute an Operational Approval, the Operational Approval in JAR-OPS 3 should take the form of an Appendix to JAR-OPS 3.346 in Section 1, rather than an ACJ in Section 2 OST 05/02

3. From the ACJ-OPS 3.346 addition proposed by HSST:- 5.If the aircraft has been certified for flight in Limited Icing Conditions, then the operator should ensure that the procedures in the Operations Manual take additional account of the following: OST 05/02

4. a. Use of the procedure is only applicable to over water (sea areas) operations departing and arriving from an offshore heliport, or airports at the coast. The procedure should not be restricted to only over-water flights because: (i) The fundamental principle applying to IFR in uncontrolled airspace is that an aircraft in IMC may descend at any time to MSA. It follows that in order for an IFR flight to be able to escape from icing conditions it is only necessary to ascertain that a layer of positive temperature air exists above MSA. OST 05/02

5. (ii) The surface of the sea has the features that it is flat and at sea level and height can be accurately measured using a radio altimeter. And Vessels, oil installations and other obstacles can be ‘seen’ on weather/mapping radars. Nevertheless MSA remains 1,000 feet above the highest obstacle within 8 km of an aircraft’s position. And An additional IFR procedure will be required for any descent below MSA. OST 05/02

6. (iii) It is true that over sea areas where the sea temperature is in the order of +5 degrees C, a layer of positive temperature air is frequently to be found between the surface and 500 feet amsl. • This, combined with the IFR procedure referred to in (ii) above provides a means of escape into non-icing conditions. • However, as indicated in (i) above, this is an extrapolation from the basic principle. OST 05/02

7. (iv) If use of the Limited Icing Approval is to be prohibited except over the sea, then – • Aircraft over land would be prevented from climbing through a sub-zero layer of cloud at, for example, 4000 ft, even when positive temperatures exist well above an MSA which might, for example, be as low as 2000 ft. • What would be wrong with a regulation according to the HSST proposal is that: • The logical structure of primary operations under IFR would be distorted by this unnecessary prohibition, while a secondary procedure with less legitimacy, involving en-route descent in IMC to below MSA, would be enabled. OST 05/02

8. b. The need for the flight Crew to use best available information to ensure that there is no unavoidable icing of a severity worse than the flight manual continuous limit along the planned route at the planned altitudes or flight levels. • “Best information” is not a precise enough term: • The best information available might, on occasion, be inadequate for flight planning purposes. • ICAO Annex 3 and the relevant Regional Air Navigation Plans specify the various types of forecast available. • Use of the Limited Icing Approval needs to be referenced to the accredited aviation forecast types e.g. Area Forecast. OST 05/02

9. The aircraft’s flight path should ensure that the time to vacate icing conditions by reaching a positive temperature band of air, or landing at the arrival airfield elevation, is not greater than the time stipulated in the Aircraft Flight Manual. The band of positive temperature air should not be less than 500 ft in depth. Offshore the positive temperature band of air should exist at or above 500 ft AMSL and onshore between MSA and MSA +500 ft. However, an onshore approach in IFR may be conducted with the zero degree isotherm below MSA providing that sub-paragraphs d and e can be complied with; • Positive temperature air above MSA will always be within reach • Positive temperature air below MSA over the sea will be within reach of a helicopter over the sea if it is equipped with radar and rad alt and there is a procedure for descent in IMC to less than 500 ft amsl. • Positive temperature air below MSA over the sea will be within reach of a helicopter making an IFR approach to an inland aerodrome if prior to the Intermediate Approach Fix (IF) it can divert to the coastline at a safe altitude and make a descent to 500 ft amsl within the flight manual time limit. Alternatively, after the IF the helicopter can complete the approach and landing. OST 05/02

10. If the approach is made in IMC and the 0C isotherm is at or below the MSA with no band of positive air above MSA, then in order to ensure a missed approach back into icing conditions will not be necessary, the minimum Cloud Ceiling in the Landing Forecast should not be less than DH/MDH + 400 ft; • e. Any descent into the band of positive air should take place over the sea or as part of an instrument procedure; • These provisions are not adequate • The ability to descend into positive temperature air (which in this example is only to be found over the sea) is a fundamental requirement, but in the case of a flight to an inland aerodrome where the zero degree isotherm is below MSA, the aircraft would need to maintain a safe height and fly for several miles and some minutes to reach the coast line before being able to descend. OST 05/02

11. Prior to loss of 1000 ft vertical separation from obstacles (on passing the Intermediate Approach Fix (IF)), the path taken by the helicopter must enable a return to be made (at a safe height) to the coastline where a descent over the sea can be accomplished within the period quoted in the Flight Manual. After passing the IF, escape from icing conditions should be accomplished by landing at the destination. However, to reduce the likelihood of a missed approach in a heavily iced helicopter with an impaired climb performance, further descent should only be undertaken if the reported cloud ceiling is higher than the DH/MDH. The references in the HSST proposal for weather minima are spurious. It has nothing to do with Landing Forecasts, or AMC OPS 3.295(c(1), which is related to flights undertaken without the carriage of fuel to reach an alternate (in that circumstance, a forecast cloud ceiling of DH/MDH + 400 feet is appropriate because it facilitates a VFR arrival after a cloud break over the sea). OST 05/02

12. In the context of an IFR arrival in icing conditions, the factor to be added to DH/MDH should be based upon a similar concept to that employed with the minimum RVR associated with the Approach Ban. i.e. The aircraft should not pass the IF when the probability of landing is low and a successful go-around may be compromised. OST 05/02

13. The aircraft should not be dispatched without a serviceable Radio Altimeter and Airborne Radar. The MEL should reflect this requirement. • It is accepted that radio altimeter and weather/mapping radar are essential equipment where reliance is placed upon the ability to descend into the layer of positive temperature air lying below MSA over the sea. OST 05/02

14. The HSST proposal makes reference to departure from an inland aerodrome in icing conditions, but states no special requirements. Given that a helicopter rotor may pick up significant quantities of ice while taxiing prior to take-off (especially if freezing fog is present) there should be checks (e.g. that hover power is within normal limits) to ascertain that: at commencement of the take-off the aircraft still remains capable of flying the instrument departure route with the necessary rates of climb; notwithstanding, that: when at a safe height the helicopter may need to divert directly to the coastline in order to make a descent over the sea if unexpectedly extreme icing conditions are encountered. OST 05/02