A recent incident reported to the ATSB highlights the hazards visual pilots face in inadvertently entering IMC, particularly as winter approaches.
Last month the pilot of a Piper PA-28 had departed an airport in regional NSW bound for a destination on the coast, a flight which would take them over national parks with wooded, mountainous terrain.
"Passing through the mountains the cloud ceiling began to lower as the terrain got higher," the pilot reported to the ATSB.
"Knowing the weather at my destination from weather cameras I decided to continue following the valley as reference.
"This caused the aircraft to become trapped within the valley with surrounding cloud on either side," they continued.
"As the cloud passed through it became lower causing the aircraft to enter IMC. Due to the surrounding mountains, I was unable to turn around, so I declared a PAN. ATC then helped give traffic advice and a lowest safe altitude to climb above.
"Shortly afterwards I was back in VMC on top of the cloud at roughly 3,000 ft and I then descended through a gap and maintained VMC for the rest of the flight to land safely at my destination."
Fortunately, in this case, with the timely assistance of ATC the pilot was able to exit IMC and land safely. But the risk of adverse consequences after entering IMC, without the training and flying an aircraft equipped to do so, is very real.
"The ATSB's database of aviation safety occurrences shows that about one in ten VFR into IMC events result in a fatal accident," said ATSB Director Transport Safety Stuart Macleod.
"For visual pilots, pressing on where there is the possibility of entering IMC carries a significant risk of spatial disorientation, where the brain receives conflicting or ambiguous information from the sensory systems, resulting in confusion, incorrect control inputs and loss of control of the aircraft."
"That is why we encourage all pilots, no matter your experience level, to develop the knowledge and skills required to avoid unintentional entry into IMC," he said.
"Have alternate plans in case of unexpected changes in weather, and make an early decision to turn back, divert or hold in an area of good weather.
"And use a 'personal minimums' checklist to help manage your flight risks."
A personal minimums checklist is your own set of rules and criteria for deciding whether, and under what conditions, to depart, or continue flying, based on your knowledge, skills and experience. As a personal 'go/no go' checklist it can help take the stress out of difficult decisions both before and during flight.
"If you don't hold a current instrument rating, you should always be prepared to amend and delay plans to fly due to poor or deteriorating weather conditions, and not to push on," Mr Macleod concluded.
"Thorough pre-flight preparation is the best defence against flying into deteriorating weather."
You can find here the ATSB 'Avoidable Accidents' publication: Accidents involving Visual Flight Rules pilots in Instrument Meteorological Conditions | ATSB
Caption: Visual pilots should make early decisions to turn back, divert or hold in an area of good weather (note, not the incident aircraft).
