Sea State Forecasting – CHIRP
The CHIRP Charitable Trust, who run the UK’s Confidential Human Factors Incident Reporting Programme, today published Air Transport FEEDBACK Issue 113. This included discussion of a report on sea state forecasting in the North Sea. The original report submitted to CHIRP was:
Post CAP 1145 [Safety Review Of Offshore Public Transport Helicopter Operations], a sea state limit has been placed stopping CAT [Commercial Air Transport] operations overseas greater than sea state 6, or 6 metres. We reported for duty one hour before flight as requested. There were no managers present despite the knowledge that the weather (sea state) was due to deteriorate during the afternoon. The Met Office website 12:00Z forecast for the sea off the Aberdeen coast showed a maximum wave height of 4.5 metres, the 18:00Z forecast for the sea off the Aberdeen coast showed a maximum wave height of 6.5 metres over the majority of the UK North Sea as far as The Shetland Isles. One of us contacted the Met Office for clarification of the forecast wave height and was told the sea off the coast of Aberdeen would have waves in excess of 6 metres between 14:00Z and 15:00Z. There was a request made for the hourly forecast charts to be faxed to us so we would have the evidence at hand if management challenged us on our decision to stop flying, but they were not willing to send us the information, only give a verbal brief. Crews elected not to depart on flights that would require a return overseas greater than 6 meters. Management accepted crew’s decision when briefed later. Lessons Learned: Crews should not have to rely on verbal conversations with forecasters and hourly forecast should be made available on the Met Office website.
It is noticeable, and very encouraging, that while the reporter was concerned that they would need strong evidence to back any decision not to fly, that the management did accept that decision without the hourly data they had requested. CHIRP commented:
The Met Office provides forecasts of Significant Wave Height on a briefing system used by offshore helicopter operators called OHWeb. Operators are required to base their planning and operating decisions on the Wave Height forecasts on OHWeb. Since the report to CHIRP was received, the time steps for the forecasts on OHWeb have been increased from 6-hourly to 3-hourly to improve the fidelity and availability of the forecasts. Although the Met Office generate the product in hourly time steps, it was decided that the provision of hourly reports would not be appropriate because they could represent a potential source of pressure on pilots. With hourly forecasts, it could be that some pilots would feel compelled to ‘design’ the flight route around areas of high sea state using successive short term sea state forecasts. Moreover, with high sea states some pilots could have a tendency to await the next forecast with the mission on hold instead of cancelling it, taking a ‘rest’ break, and replanning it thoroughly. Despite the introduction of 3–hourly forecasts there remains the potential for actual sea states to be higher than those forecast; when this occurs the N Sea operators confer over the source, number and reliability of the reports before making a collective decision to operate, postpone or cancel flights.
It is not clear from the text above who made the decision to only issue 3-hourly forecasts. The issue of significant wave height and sea state is relevant both to aircraft ditching capability (which Aerossurance has discussed previously) and in relation to successful rescue. The current UK Civil Aviation Authority’s (CAA) current Offshore Helicopter Operations Safety Directive is SD-2015/001. The UK CAA have now issued CAP1243, the Offshore Helicopter Review Progress Report, which provides an update on progress with CAP1145 to 31 Dec 2014. Aerossurance reported on CAP1243 earlier in the week.
UPDATE: Aerossurance has also discussed trials with high frequency radar to monitor wave height. The more extreme sea conditions can be seen in this footage from a North Sea Emergency Response and Rescue Vessel (ERRV) of the Good, the Bad, and at 3min 20sec, the Ugly in that aftermath of a hurricane:
Aerossurance is an Aberdeen based aviation consultancy. For expert advice on offshore helicopter design, operations survivability and safety that you can trust, contact us at enquiries@aerossurance.com
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