Offshore Transit with Icing Risk and Single-Engine Contingency
You are planning a 60 NM overwater transit at 2 000 ft in a twin-engine helicopter. Forecast en route temperature is −2°C with visible moisture and a freezing level at 1 500 ft. The aircraft has anti-ice protection for the engine intakes and pitot but no rotor blade de-icing. One engine is a recent overhaul with 10 hours since installation. The destination platform has a 20 kt crosswind limit and the current wind is 25 kt gusting 35 kt. Fuel gives 2 h 10 min endurance; the transit takes 45 min. There is no alternate platform within 30 NM, and the sea state is 4 m.
1. Assess the icing risk and decide whether the transit can be conducted at 2 000 ft or whether a different altitude or route is required.
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Icing assessment:
- The freezing level is at 1 500 ft, so 2 000 ft is above it and the temperature is −2°C with visible moisture - this is a classic icing environment.
- The aircraft has engine intake and pitot anti-ice but no rotor blade de-icing. Rotor icing degrades lift and increases vibration and power required; it can develop quickly and is not detectable by the available protection.
- Decision: Do not transit at 2 000 ft in visible moisture. Options: climb above the cloud tops if a clear layer exists and performance allows, descend below the freezing level (below 1 500 ft) if terrain and sea state permit, or delay until conditions improve. If no option is available, cancel the transit.
Reasoning: Without blade de-icing, the aircraft is not certified for flight into known icing. The presence of visible moisture at −2°C is known icing. Proceeding would be a clear violation of the flight manual and a serious safety risk.
2. Evaluate the single-engine contingency and crosswind landing at the destination, and state the decision.
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Single-engine contingency:
- The recent overhaul with 10 hours since installation is a reliability concern; an engine failure during the overwater transit would leave a single-engine helicopter over water with no alternate within 30 NM and a 4 m sea state. Ditching survival is unlikely to be rapid.
- Crosswind: The platform limit is 20 kt and the wind is 25 kt gusting 35 kt, which exceeds the limit. A landing would be outside the aircraft's crosswind capability.
Decision: The transit should not be conducted as planned. The crosswind alone exceeds the platform limit, and the icing environment plus single-engine overwater risk make the flight unacceptable. Options: delay until the wind drops below 20 kt and the freezing level rises, or use a different platform with a more favourable wind. If the flight is time-critical, consider a different route below the freezing level with a closer alternate. The correct judgement is to hold and reassess rather than press on.