VFR into IMC

VFR into IMC refers to a flight conducted under visual flight rules (VFR) operating below VFR minimum conditions where visual references may be lost by the pilot. This includes operating in and around cloud, fog, rain or smoke.

So, I flew through a bit of cloud, what’s the big deal? 

VFR flight into IMC is the cause of 1 in 10 fatal accidents not only within RAAus but within all fatal accidents in Australia.

When operating within IMC, you no longer have a visual reference of the horizon which typically accounts for 80% of the input required for human orientation. Your body attempts to maintain orientation by using the vestibular system within the inner ear to detect changes in pitch, roll, yaw and acceleration/deceleration – Unfortunately, as humans, these internal systems are inherently flawed leading to a false sense of information and quickly resulting in spatial illusions and disorientation. 

Next time you are flying with an instructor, ask them to monitor the flight as you close your eyes and attempt to maintain straight and level flight. How long do you think you can maintain straight and level – 2 minutes, 3 minutes? Chances are you will start to deviate in only a matter of seconds - You’ll be amazed at how quickly stable flight is lost. This is exactly what happens when pilots enter IMC, quickly leading to loss of control of the aircraft.

This area is particularly close to my heart as I recall one particular day operating as a skydiving pilot within New Zealand.

The day started like many others, standing on the ground, staring at the sky, speculating as to whether the clouds would open up enough to commit to our first skydive load. After much toing and froing, although marginal, the decision was made to proceed, the aircraft was loaded with 8 tandem masters and their passengers and we took to the skies above the beautiful Lake Taupo.

On this particular day, the GPS used to calculate wind speed and direction on the climb was inoperable so I resorted to conducting 360 degree orbits taking my highest and lowest ground speed in order to calculate wind direction and speed. Little did I know at this point that the holes in the swiss cheese were starting to align.

On climb, while attempting to orbit and remain clear of cloud, I was distracted by the process of monitoring my GPS, identifying ground speeds, writing down my results and attempting to make calculations to identify wind speed. I glanced up only to realise we were entering cloud. Unphased, I continued momentarily with the expectation that I would quickly exit IMC, however this was not to be the case. I transitioned to my instruments rolled onto a level heading, and in doing so, everything inside my body screamed that I was making a turn in the wrong direction. I then did something that I would live to regret - I followed my instincts, failed to trust my instruments, and reverted back to the safe feeling of equilibrium by once again turning to the left.

This is where things quickly deteriorated. Suddenly my airspeed started increasing, I pulled back on the stick and the airspeed raced backwards towards the stall. I pitched forward in an attempt to maintain airspeed however this quickly got away from me again now racing towards Vne. I was confronted by high G-forces, erratic changes in airspeed from 170kts to 60kts in a matter of seconds, and no longer had any sense of what direction was up, and what was down. Now in a fight or flight scenario, I turned back to my instruments to find my artificial horizon toppled. I managed to identify my direction of turn from my direction indicator (DI) and slowly made a turn in the right direction to regain level flight, and while doing so, broke out of cloud now several thousand feet below where the ordeal began.

So what went wrong? I was an instrument rated pilot carrying out a flight that I had conducted hundreds of times before. The occurrence would continue to run through my head for days and weeks following, asking myself, how could I let this happen?

So let’s take a look at the science: Whilst on climb in a constant radius turn to the left, the fluid within my inner ear had now stabilised and the hair cells within my cochlea and semicircular canals began to stand upright, indicating to my brain that I was no longer in a turn. Upon entering cloud, I switched to my instruments, started to ease out of the turn at which time the fluid within my inner ear moved in the opposite direction falsely indicating to my brain that I was now entering a turn to the right. With my body now leaving me disoriented I turned back to what felt like straight and level, which in fact was now a turn back to the left as I entered an uncontrolled spiral dive. 

This situation provided me with the harsh realisation that had I have not been able to eventually fight my instincts to trust my instruments, and had the cloud base been closer to terrain, then it very easily could have resulted in a collision with terrain. Alternatively, it could have resulted in overstressing the aircraft to the point of structural failure.

Research conducted by the University of Illinois in the 1990s found that when 20 VFR pilots were tested in simulators, every pilot lost control of the aircraft. The only difference between pilots was the time taken to lose control of the aircraft which ranged from 20 to 480 seconds – This average of 178 seconds is now commonly referred to as 178 seconds to live.

So what does this mean for VFR pilots? In essence, Do NOT fly into IMC!

As pilots we often feel pressured to continue with a planned flight. Perhaps someone else needs to use the aircraft. You may be heading home from a weekend trip and need to get back for work tomorrow. Or simply, you are in flight and so close to home – It would be a waste to turn back now!

These are common situations where pilots find themselves pressing on into deteriorating conditions which result in being caught off guard. Sadly, this results in many pilots not making it home. In the event that you do end up within poor conditions, it is always best to carry out a precautionary landing, even if this results in damage to the aircraft, than to press on and get caught in cloud. An aircraft may be repaired – A life cannot! 

Top tips to avoid VFR into IMC

  • Conduct thorough pre-flight weather planning prior to flight and obtain updated reports where possible
  • Avoid pressure to continue with a flight if conditions are marginal
  • Avoid the potential for complacency by not conducting thorough planning when flying a familar route
  • Have an alternate destination in case weather conditions deteriorate
  • Make the decision to turn around early, even if you are close to your destination
  • Check that conditions are not closing in around and behind you
  • If conditions continue to deteriorate, carry out a precautionary landing in a suitable location.
  • If you find yourself above cloud, do not hesitate to contact air traffic control for directions or assistance (admitting you have made a mistake is better than not making it home).

In the event you do inadvertently enter IMC – Do not panic. Maintain a scan on your instruments and avoid becoming fixated on any one instrument. Make a gentle turn back out of the cloud (in the direction of lowest terrain) and request assistance from air traffic control if available.

For more detail on the information contained within this article, see Flight Safety Australia’s article on VFR into IMC at: https://www.flightsafetyaustralia.com/2016/01/178-seconds-to-live-vfr-into-imc/


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