What is the All Weather Capability ?
Normally referred to as IFR (Instrument Flight Rules) capability, it basically means
the upgrading of the aircraft cockpit with instrumentation necessary for flight in bad weather.
In fact the first thing to remember is it is not strictly 'all-weather'. You can let
down through cloud to an airport equipped with the appropriate aids, but you need specialist
equipment to enable you to make a safe approach to a company car-park or a back garden in poor
conditions - and you must be able to see something on final approach. That is a fact which
some new corporate owners discover to their cost on the first murky day they encounter.
This apparent restriction is because most cockpit instrumentation merely allows you to
interpret ground based signals; those which are approved by the Civil Aviation Authority
to provide information to aircraft. If the specific location has no aids, then no signals,
so no go. There are weather limitations to these navigation aids as well. Some airliners
can land at some airports in zero visibility, but in general - although instruments
can provide accurate navigation to overhead a specific location - such feats are beyond
helicopters and car-parks at present. New avionics equipment based on GPS
(Global Positioning System) or MLS (Microwave Landing System) is helping
to remove these restrictions.
Icing is another factor which can limit helicopter operations. The temperature need
not be freezing at surface level for there to be a real risk of icing at height. This is
routinely forecast, but if the weather is cold and there is cloud on the route icing may
be a problem.
In the UK, IFR also means two engines. It is a legal requirement by the CAA (Civil Aviation Authority) that all
IFR helicopters are twins
So what are the advantages that all this extra expense brings ?
Firstly, it is safer to fly under IF Rules in bad weather than it is to struggle along in marginal VFR (Visual Flight Rules) conditions underneath. Every helicopter pilot has had the experience of fumbling his way along at low level, his eyes popping out of their sockets as he looks for power lines, factory chimneys, rising ground etc., in an attempt to get to his destination. Airborne weather forecasts are sometimes wrong too. The situation is full of traps for the unwary or unprofessional.
IFR Capability gives the pilot an escape route out of this situation. He can fly up into the cloud and call for assistance. A classic example can occur when crossing water when the cloud base or freezing level lowers, visibility worsens and the pilot suddenly finds himself in a goldfish bowl of murk at very low altitude, unable to distinguish the water surface. In this situation the IFR helicopter is able to take the safe way out - up. The single can also go up of course, but he may be jumping from the frying pan into the fire.
IFR qualifications are difficult and expensive to come by. Pilots who have such ratings generally know their aircraft better, and therefore tend to be at the higher end of the competency curve.
IFR capability allows a considerably higher utilisation of the helicopter, and therefore makes it a more cost-effective aircraft.
A twin engined/IFR layout gives the helicopter far more freedom, especially when it comes to flying over congested areas. A single engined machine must always fly over a route where it may land safely in the event of an engine failure. A twin can normally continue safely with its remaining engine.
Back to Articles Index
|
|
