The RNLI's lifeboats are part of the UK's overall Search and Rescue Facility and often work closely with their airborne counterparts.

Jim Ferguson, press officer of the Aberdeen branch of the RNLI, looks at HM Coastguard's helicopters - with some advice on what to do in the event of a helicopter rescue. The British government's criteria for search and rescue (SAR) helicopter coverage requires aircraft to reach any point up to 40 miles offshore within one hour by day and 100 miles within two hours by night.

To meet their commitments, HM Coastguard currently spends some £9m to operate a contracted fleet of four Bristow Sikorsky S-61N helicopters, based at Sumburgh, Stornoway, Lee-on-Solent and Portland; the Irish Department of the Marine maintains a similar Bond helicopter at Shannon.

In 1996 the UK-based aircraft flew 625 missions, bringing the total number of calls handled by HMCG, Irish and British oil company helicopters since the first (Bristow Whirlwindequipped) unit was formed at Mansion in 1971 to 6,600.

Also heavily involved in maritime SAR helicopter tasks are two Royal Naval units, with Westland Sea Kings at RAF Lossiemouth, Boulmer, Leconfield, Wattisham and Chivenor, and the Westland Wessex of RAF Valley and two Irish Air Corps units operating an Alouette at Baldonnel/ Casement and a Dauphin at Finner Camp.

Shell Expro's Bristow Bell 212 is also available in the East Shetland Basin and, if necessary, HMCG can call on additional units as required.

Coastguard and military helicopters are normally at 15 minutes' readiness between 0730 and 2100 daily, reducing to 45 minutes at other times, although typical reaction times are somewhat less.

The normal operational radius of the S-61N (a slightly larger variant of the Sea King) is around 150 miles at a 110-knot cruising speed and endurance is a near to four hours - including 30 minutes on task. It also has a fuel dump facility to bring it down to hover weight.

The usual flight crew is Captain, co-pilot, winch operator and winchman/woman, all of them more than meeting their contracts' demanding experience requirements and all wearing immersion suits and helmets.

Equipment The S-61N's cockpit instrumentation is virtually to jet airliner standards, with an equally comprehensive range of specialist role and communication equipment which has been developed to handle all aspects of long-range/all-weather SAR tasks.

Flight instruments include dual radar and barometric altimeters, GPS linked to the basic navigation suite, multi-functional situation and engine instrumentation, automatic flight control system with auto-hover, search and weatherradar, instrument landing system, winch controls, cockpit voice and flight data recorder, two 14-person Helirafts and a portable 180gpm diesel pump.

Communication equipment is equally sophisticated: dual VHF(AM) radios, VHF(FM) radio, HF radio, UHF radio, (all with homing facilities) and individual crew beacons. A Forward Looking Infra Red (FLIR) package is also fitted and is capable of detecting minute temperature difference between, for example, a floating survivor and the surrounding sea.

The standard winch cable length is 300ft with a maximum load of 600lb and variable hoist speeds - this is normally controlled by the winch operator, but can be controlled remotely by either pilot.

Although most approach, hover and position information is provided in the form of a 'running commentary' by the winch operator, he or she also has a limited horizontal facility at the door position.

The core of the Bristow system is its autohover package which, when manually set with the datum, has the aircraft complete a circuit and then come to, and hold, an into-wind hover over the position at any pre-set altitude between 40ft and 199 feet.

Apart from normal winching techniques, aircrew will often opt to carry out a 'highline transfer', in which a thin 150ft cord is attached to the end of the winch cable and lowered from overhead.

This is typically used for yachts or vessels with cluttered top hamper and in heavy sea states. The line is pulled in by the casualty as the aircraft descends to a suitable lower level and the transfer of people or equipment then continues in the normal way.

The manoeuvre is exercised regularly on training flights and all seafarers of whatever discipline would be wise to have at least a basic knowledge of its workings.

The S-61N's capacious interior (during one rescue, the Sumburgh helicopter was carrying no less than 31 survivors!) means that there is adequate space for aircrew, winch position, FLIR display, boxes of specialist equipment, long-range tank, two observation positions with bulged windows - as well as passengers! The aircraft's winching position is just aft of the cockpit, so downwash is rarely a problem when dealing with small craft, although varying the machine's height will often help.

Up to three stretchers, capable of being slung from the winch cable, can be carried plus a comprehensive first aid kit - some of which is contained in backpacks so that it can be lowered to the casualty. There are also portable and fitted Entenox and oxygen cylinders, a defilibrator, blood transfusion and pressure monitors, suction equipment and so on.

All aircrew have undergone and remain current in advanced first aid skills, some to paramedic standard and, if required, health authorities can provide a doctor.

On the receiving end Captain Paul Bentley, Bristow's Sumburgh Chief Pilot, says: 'Simply put, do as we tell you, no more,no less. Secure all loose gear and lines as best you can before we arrive. If you have a radio, then we will brief you on what we require you to do; if not, then follow aircrew hand signals or read blackboard messages.

'Never, ever secure the winch cable or highline - if either should part, they can fly up into the rotor discs with potentially lethal consequences.

'Don't attempt to grasp the winchman to help him aboard, otherwise you risk acting as an earth for the helicopter's static electricity, and don't fire flares or rockets when we are close to you.

'Listen to what the winchman tells you, and if you're not sure, ask. When in the strop, keep your arms firmly by your sides, otherwise you run the risk of falling out.

To sum up: keep calm and let us get on with it.' The techniques used by the Military helicopters may vary slightly, but are generally similar to those described and used by the Coastguard helicopters.AND LOOKING UP...

Mike McHugh is now the RNLI's Trials Team Coxswain, which, combined with his past experience as Staff Coxswain, means he has probably seen the underneath of as many helicopters as anyone...The first thing you'll notice when a helicopter comes overhead is the noise it creates and the downwash from the rotors.

If you're not used to it. it can completely disorientate you, but we exercise so often with the helicopters that we're thoroughly acclimatised to it.

'Just as the crew of the helicopter ask.you to trust them and get on with it, do the same on the lifeboat. If you're going to be hoisted from our deck then the crew will have you in the right place at the right time and help the winchman get you into the strop.

'Normally we're asked to steer a particular course and speed, if the weather and sea allow, so that the helicopter has a suitable headwind to fly into.

'The helicopter's door and winch is the starboard side, so he'll come in over our port quarter while we hold a steady course. If we veer off to port he'll lose sight of us, which is pretty tricky for him! 'We can winch either from the foredeck or the aft deck, depending on the lifeboat and the conditions.

The coxswain will be overseeing the whole thing, with a helmsman on the wheel and another crew member acting as 'flagman'. He'll be at the opposite end of the lifeboat to the winching, standing where everyone can see him, because unless there's a co-pilot in the helicopter or an emergency there won't be any radio communications during the winching. The pilot is already receiving a constant stream of information from his winchman.

'Holding up the red flag means 'don't winch' or 'break off winching' while the green flag means it's OK to start and to continue. The green is held up all the time the winching is taking place, to confirm everything's OK and also to give the pilot an indication of the wind direction.

'It'can also be a bit worrying the first time you're lifted off - one minute you've got your feet on a deck that's going up and down the waves and the next thing you know is that you go up... and just keep going! 'Don't wriggle about, just hold your arms down at your side like you've been told, and don't try to help yourself. When you arrive at the aircraft the winchman takes over He'll turn you round and pull you in through the door in a sitting position - making sure that you don't hit your head on anything.'.