Very few VFR pilots enter cloud intentionally but nonetheless anyone can very easily discover the perils of inadvertent IMC
reproduced from GASCO

Crashing into a cloud stuffed hill in this sort of aircraft is usually fatal

Not many aeroplane occupants survive a VFR (Visual Flight Rules) into IMC (Instrument Meteorological Conditions) accident; microlight pilots and passengers fare somewhat better because of the lower inertia at the final impact, but with the latest designs of microlight offering far higher speeds and lower drag, this difference is likely to diminish in future. VFR only helicopters, however, have an even greater need to avoid IMC than do VFR only aeroplanes; the inherent instability of the rotary wing machine means that loss of control in IMC will occur far more quickly than it will in a fixed wing aircraft. The daunting statistics alone might be thought to be sufficient to convince nearly all VFR pilots of the foolishness of venturing into IMC, and yet they continue to do it.

Crashing in this sort of aircraft offers a better chance of survival - but not that much better

However, if you ask around VFR pilots whether they make a practice of venturing knowingly into cloud, they will tell you universally that they do not. Some fixed wing pilots will have made a hesitant exploration at some time into the interior of some small fluffy cumulus cloud, just to see what it was like inside, but beyond that, VFR only pilots do not seem to be the least bit attracted to non visual flight. So how is it that the accident reports often include an account of some unfortunate VFR pilot or other getting into a nasty scrape or even dying as a result of flying into cloud?

You will not keep control for many seconds if you suddenly find yourself in IMC in a small helicopter

The simple answer is that few if any of them ever intended to get into cloud in the first place. While the regulations conveniently divide our airspace into those parts where you can easily see where you are going and those where you cannot, in real life, in British airspace, there are sometimes uncertain areas where it is VMC one minute, and IMC the next. You can easily investigate such areas with relative immunity from risk by driving your car along a road over high ground on a day with a low cloud base. You may well find yourself entering and leaving cloud without any change in altitude. Stop your car somewhere safe and watch what the cloud base does. Often it is not constant but as clouds billow over ridges the base rises and falls. If you are willing to accept a bit more risk and are suitably equipped and experienced, try some hill walking.

You will discover that in addition to the phenomenon of the cloud base that rises and falls, clouds actually form as if from nowhere and sometimes dissipate with equal speed. The risk of suddenly becoming enveloped in cloud is well known to hill walkers and mountaineers and accepted as an event against which precautions must always be taken. The simplistic view of the pilot, however, is that cloud is something that you fly into, rather than something that can sometimes form around you when previously you were in adequate VMC.

So UK pilots have to accept that IMC can sometimes envelop them even when they had never intended to fly in such conditions. The likelihood of this occurring is greatest when flying low level and is far more common in hilly country than over flat terrain. If you want to avoid the risk you should avoid flight conditions where the cloud base is less than 1,000 ft above flat terrain and a good deal more than that over hills. The oft repeated, cloud covers hills, in met forecasts is a condition to avoid because hills often act as a magnet for clouds, drawing the base down so as to cover the peaks.

It is scud running that so often converts VFR into inadvertent IMC. Most VFR pilots with more than a few hundred hours have been caught out in this way and will probably not want to relive the experience. The trap is so easily entered. It is only ten minutes or so to home, the cloud base is lowering but you feel that probably you will be able to scrape through underneath the cloud and the alternative of turning back and diverting to somewhere you did not want to be seems far less attractive. Your GPS set boosts your confidence in your ability to find your way home through the murk. This is a classic moment when pilots sort themselves out into the professionals and the chancers.

All light aircraft flying is risky - at least as risky as motor cycling - but if you press on into a lowering cloud base, navigation is going to get more difficult the lower you get, aircraft handling is going to become more difficult because of increased turbulence, stress levels are going to rise and in motor cycling terms you are now into black ice conditions. If you next hit fog on your motor bike you are going to be in real trouble, but at least you can then slowly pull up and stop. If you hit IMC when scud running you do not have that final option.

You have to keep flying, you know not where, and if you do not fly into the hill that probably attracted the unusually low cloud you will next have the challenge of keeping the aircraft flying without any visual reference. Getting yourself into this very dangerous position is something to avoid, as those who have been there and survived will confirm. There is no measure that is guaranteed to save you. If you are a fixed wing pilot the 180 degree turn under instruments may work, but only if you do not hit the hill on your way round behind you where previously it was VMC. Descending and turning away from the supposed position of the hill might work or, alternatively, turning East and facing your maker could be your best plan. You have reached a position where only luck is going to save you and your passengers.

Never attempt scud running in this sort of terrain

There is only one universal rule that is likely to keep you safe, and that is to avoid getting into low level scud running in the first place. Any organised pilot has in mind specific weather minima, actual or forecast, that they impose when making the go/no go decision before going flying and whatever those minima may be, you must have the self discipline to accept the same when wondering when en route whether to press on or turn back.

There is an alternative rule available only to those who fly aeroplanes that are equipped for flight in IMC, and that is also to equip yourself with at least an IMC Rating so that you have another answer to the lowering cloud base. And that is to climb under IFR to the Minimum Safe Altitude or higher and then sort matters out from a position of renewed safety. Those 12 hours of IMC training could one day make all the difference to your survival if you become one of the many UK pilots who suddenly find themselves caught out in inadvertent IMC.

Reggie Bender always says that the advantage of scud running is that at least you can read the road signs

Nigel Everett