INADVERTENT ENTRY INTO IMC

Acknowledgements: Astral Aviation Consulting & CAA Skybrary

I-IMC is a situation where pilots lose visual contact with the ground due to deteriorating meteorological conditions. Why does the loss of visual cues we suffer when we inadvertently enter IMC have such rapid and disastrous consequences? It’s all to do with spatial disorientation .... Keeping yourself oriented in VFR flight is easy - you have visual reference to a horizon outside the aircraft; therefore, your eyes can easily work out which way is up ... But when you lose that horizon, 80% of your orientation goes with it. But that’s okay, your inner ear and seat of your pants will help … won’t they? Sadly, they can make it worse ... Without that visual backup, the inner ear can be easily tricked into thinking you’re not turning, when in fact the aircraft is gently rolling but at a rate that your body simply can’t pick up! ... So, if you do end up in IMC, you need to ignore your senses, trust your instruments, and concentrate on flying the aircraft, as your life depends on it!

How can these events happen to us?

The risk comes from one or both of two main areas:

·       Errors in pre-flight planning, meaning unsuitable weather conditions during our flight are not anticipated ... due to deficiencies in knowledge or training ... or as the result of human error, such as perceived pressure, fatigue, distraction, or complacency. 

·        Errors during execution of our flight which cause us to continue into unsuitable weather ... a loss of situational awareness causing us to fly into bad weather, or to allow bad weather to develop around us without acting, due to complacency about our ability ... we may believe we can cope, or ‘have got away with it before’... There may be peer pressure from other pilots, or with the pilot in command ... or pressure to get back home, or to get a rental aircraft back to base ... or to complete a promised flight with passengers who often may not appreciate the risks involved.

How can we avoid these events happening to us?

During pre-flight planning, we should obtain and understand:

·       An area forecast covering the general frontal situation, cloud and freezing level that will affect our flight ... Are there any local threats such as CBs in the forecast? 

·       A forecast of the wind speed and direction for the departure, route, and arrival ... Is it going to be within our comfortable limits? ... Is it associated with changeable weather situations that could catch us out?

·       Relevant TAFs and METARs for departure, route, and arrival ... Even if our airfields don’t publish their own, nearby airfields can be great indicators of likely conditions in the area ... what PROBs are there that could happen? 

Aids such as Skydemon and Airbox can provide excellent route briefings and up to date information ... 

In flight, look ahead to spot poor weather on our intended route ... a continuing need to descend to maintain ‘clear of cloud’ is a key indicator that we are potentially likely to Inadvertently enter IMC to avoid CFIT ... In any case, when becoming aware of worsening conditions, an early move to alter route, turn back, or divert is critical! 

At or Below 3000ft AMSL and 140kts IAS, 1500m visibility is legal for UK Class G VFR flight. However, most VFR pilots will find anything below 5km visibility very challenging ... the lack of a natural horizon and visible navigational features can make workload extremely high and increase the risk of disorientation. 

What should I do if I inadvertently enter IMC?

Once you recognise you are losing visual references, the priority is to have a plan ready to regain visual conditions, and to stay in control. You must make a firm decision to trust and control the aircraft by using the available flight instruments: 

·       Concentrate on the attitude indicator as your primary instrument

·       Maintain the correct attitude for straight and level flight

·       Keep the wings level, to prevent a spiral dive and departure from controlled flight

·       Limit looking away from the attitude indicator to glance at other instruments 

·       Only make small, progressive control inputs 

·       Consider the escape plan; is a 180 turn appropriate? ... if so, are you at a safe height for the terrain? If not, climb before turning ... gently select the turning attitude on the AI at a bank angle of about 15 degrees ... some back pressure may be required to prevent the nose pitching down ... maintain concentration on the AI, with occasional glances at the DI ... after reaching your desired exit heading, gently roll the wings level ... maintain straight and level until back in VFR 

·       If the 180 turn does not recover the situation ... Seek early assistance from ATC or D&D ... a MAYDAY call will often be most appropriate ... make clear you are in I-IMC and not qualified or trained to fly in it ... follow ATC assistance and accept you may need to turn, climb, or descend under their instructions to recover the situation

If you start to lose control when in IMC, you should accept the situation and take prompt action to recover straight and level flight. If you are in, or entering, an Unusual Position or Unusual Attitude, you should:

·       SPEED – check speed and adjust power setting

o   Speed low or decreasing – set full power

o   Speed high or increasing – set idle power

o   Speed stable – leave throttle at current setting but monitor

·       ROLL – roll the wings level using your attitude indicator

·       PITCH – select level flight attitude on your AI, hold and check in trim, then adjust power to around normal cruise setting and assess what happened. 

You may want to carry out some post recovery HEROS checks to help keep you safe:

·       HEIGHT – am I at a safe height? Do I need to climb to get to MSA and away from terrain?

·       ERECT – are my instruments erect and working? Can I trust them?

·       REASON – why did that happen? Is something not working or wrong? Could it happen again? Check CO monitor if I have one – is CO poisoning a possibility? 

·       ORIENTATION – where I am going now? Where do I need to be going?

·       SEEK HELP – if not already, get onto a suitable ATC agency or D&D and declare a MAYDAY and seek assistance. 

Summary

Remember, if at any stage you get that inner monologue saying ‘it will probably be ok’ then stop and think, am I doing the right thing? Disappointing passengers, or a night in a hotel somewhere may be the best option that day! 

FLY SAFE!