Dealing with a mid-air emergency in the PA28

Some months back, I was flying my family to North Wales for a holiday when I suffered a mid-air problem with the aircraft.  I declared ‘pan-pan’ and diverted to Wellesbourne Mountford Aerodrome.

Prior to take off, the pre-flight checks were completed with nothing concerning found.  I did notice that the carb heat lever was a little stiff to operate, but it didn’t ring any alarm bells.   My husband and 9 year old son were in the back, and we’d set course for Hawarden.  We were approaching half-way through the journey, and had cleared the IMC conditions that had made the start of the trip fairly intensive.  I was on an inbound course to the Daventry VOR talking to Brize Radar.  

At about this point, my son started to get a little restless, and was complaining about feeling a little unwell.  I was contemplating whether this was going to be a problem and offered him a drink.  Throughout the flight, I had been conducting regular FREDA checks, including the application of carburettor heat.  On the last few occasions I had applied it, I was concerned that the RPM wasn’t dropping very much (a drop in RPM indicates that it’s working). I think the size of the drop can vary, depending on conditions and so I convinced myself that it was fine.

About 10 miles south of the DTY VOR, I tried to apply carb heat again, but this time the lever would not budge.  I gave it a little more force, but it still wouldn’t move.  It certainly wasn’t working now.  Maybe it hadn’t been effective for some time.

Carburettor heat is used on these old piston engine aircraft to melt any ice build ups in the carburettor venturi.  You can read more in this safety sense leaflet from the CAA.  It’s a particularly prevalent problem in climates such as the UKs, and is a common cause of light-aircraft engine failure here.   If it hadn’t been working during my flight, then ice could have been silently building up in my engine.  Carb heat is usually applied in the UK at roughly 15 minute intervals during cruise, just before descent and during a low power descent.  I certainly couldn’t continue my journey, because if ice hadn’t been building up, it most likely would in the hour of flight remaining.

I had planned my course to fly abeam Wellesbourne Mountford Aerodrome.  This was in case we needed to make a comfort stop during our relatively long flight.  This was now going to be my diversion aerodrome in a rather urgent situation.  

I set my intercom so that my passengers couldn’t hear me, and then I told the Brize controller that I had a problem, and was diverting to Wellesbourne.  He asked if I was declaring an emergency.  I quickly figured that I would need to fly a constant descent approach to Wellesbourne to avoid low power settings at low level, and would require no delay, and so I declared pan (a state of urgency, but not a mayday).  Brize told me to squawk 7700 (the emergency transponder code) and they tried to make contact with Wellesbourne, and spoke to Distress & Diversion.  D&D is the UK military service that assists aircraft that are lost, in distress or need help diverting.

Because carb ice forms more quickly at low power settings, I knew that the descent and approach to land was going to involve risk.  As soon as I was to close the throttle, any ice that has built up in the system could have blocked the flow of fuel/air straight away.  For this reason, I began a slow descent at cruise power RPM, and judged my descent path so that I could make the runway, even if the engine quit on approach.  Normally, you would descend to circuit height (roughly 1000ft above ground), then circle the aerodrome to some extent before positioning to land.  That just wouldn’t have been a good idea given the state of the aircraft.  

I told my passengers that we were going to make a short stop at Wellesbourne.  My husband knew that hadn’t been the plan, but didn’t question why.  We jointly kept everything calm, and vaguely normal so as not to panic our son.  I instructed my son to pack away his video game and magazines, and told them both to check that their belts were tight.  Loose objects were packed away.

Brize passed me onto Wellesbourne, who they hadn’t been able to reach, and so I began my call “PAN PAN, PAN PAN, PAN PAN, Wellesbourne Information, G-XXXX, PA28 on route to Hawarden from Biggin Hill with carb heat failure, Daventry, xx thousand feet, diverting to you.  3 POB, aircraft colour xxxxxx.  Wellesbourne gave me the aerodrome information, and requested more information about the nature of the problem.  I positioned high right base, and practically glided down to the runway.  It was one of my best ever landings!  An emergency vehicle followed me as I taxied to parking.  

Coventry aerodrome had seen my 7700 squawk and had phoned Wellesbourne to let them know I was coming.  Distress & Diversion had also been on the phone to them too.  It was amazing to see everyone working so well to improve the chances of success.

I found maintenance at Wellesbourne, who diagnosed a perished grommet in the carb heat mechanism.  Within an hour, it was repaired and we were on our way again. 

I found that in handling this urgency, I was able to stay calm and focussed.  I had the added complication of having passengers on board, and so I was grateful for the [pilot] isolation function on my intercom, so that I could avoid them suffering any unnecessary alarm.  I’m glad that I had planned my route to fly near to various aerodromes en route, and had the Pooley’s guide in the cockpit with me.  I’m also pleased that I was free of the London TMA, and was high enough to give myself time in the event that we suffered an engine failure.

The lesson learned here was that the aircraft had been trying to tell me there was a problem, but I hadn’t been listening.   The clues being the stiff carb heat lever during pre-flight checks, and only small drops in RPM on application of carb heat during cruise.  If I had recognised these subtle, yet abnormal indications sooner, I might have reduced the risks further, or might not have taken off at all.