A Flying Recollection (Don't Try This at Home)

 

On my morning walk this morning, in the anti-cyclone that Paul Hudson had said would bring fog, I paused in the still sunlight to take in the view to the south east which was dominated by the eerie vertical emission from Drax Power Station.  I recalled earlier times when 3 huge power stations heated the air to the South, Ferrybridge, Eggborough and Drax, the last one built.  They were all slightly different and my student pilots soon came to recognise the distinct features as an aid to visual navigation.  However, at this time of year, the three stations had an even greater navigational significance.

Fifty odd years ago, the anti-cyclonic gloom that was a feature of high pressure over the Vale of York could put paid to flying instruction for days.  The visibility was progressively reduced by the accumulation of pollution which became trapped in a temperature inversion – it was useless weather for flying instruction which normally required a decent reference to the natural horizon.  Provided one could find one’s way back to the airfield, however, there was some air work that could be done above the clouds.  Above the inversion, above the blanket of fog and stratocumulous cloud, one invariably encountered gin clear bright blue skies which were perfect for flying instruction.  Finding your way up was easy but  getting back down was more problematical, particularly in the Chipmunk training aircraft which had no navigation aids, basic air-driven instruments, an engine prone to icing and only a single radio set. Neither, in those days, was there any significant ground-based radar to lend a hand with navigation.  In emergency, one could put out a “Pan” call on the emergency frequency of 243.0.  The transmission would be intercepted by a series of geographically displaced receivers and plotted by an emergency control room at the air traffic control centre with the triangulated aircraft position displayed on a large map.  Most of the time, provided one was in range of the network of transmitters and high enough to be heard, the controller would be able to relay a fairly accurate position.  But this was a last resort and not expected to be used for routine navigation.  Here greater cunning was required.

The one thing that would break the anti-cyclonic inversion and mix the dirty air below with the rest of the atmosphere above was heat.  Heat from the sun would be absorbed by the earth the resulting radiation would then heat the air above its dew point and burn off the fog.  The rising air would take all the low-level crud and mix it with the clean air above.  That was the theory but, as the sun sank lower in the depths of winter, the amount and duration of heating reduced and became ineffective.  The fog just got worse.  This was the phenomenon known as “aircrew sunshine” – the peaceful interludes allowing busy instructors time to write their student reports, drink coffee and hang around the crew room until the Flight Commander determined that it was time to stack for the day and go to the bar.  There was time to attend to physical fitness because, sometimes, we walked to the village pub.

Nevertheless, there was fierce competition to make the best of the weather and if one could get one’s student into the air and achieve something then there was kudos to be won.  The big trap was the so-called, “suckers’ gap.”  This was the meteorological phenomenon when the weak sun managed to penetrate the grot and begin to heat the lower atmosphere.  The heating raised the cloud base and often raised the spirits by revealing a lightening in the sky.  “Can’t be long before this lot clears completely,” the sucker would think and rush to the flight-line in an attempt to be the first one airborne.  Unfortunately, the little stirring caused by the sun’s heating would actually cause colder air above to circulate and replace the warmer air below – result back to fog and embarrassment for the sucker.

So back to my walk and my view to the south and I recalled one murky day at Church Fenton when I had scratched my way through fog and layer of low cloud to burst out (if bursting out is appropriate for the Chipmunk rate of climb) above the tops to a perfect blue sky on top of a flat brilliant white cloud carpet.  It was one of those visual sensations that stay with you for ever and, in retrospect, one of the immense justifications for becoming a pilot in the first place.  When it was time to come down I could have chosen to make a “controlled descent through cloud” using ground based direction finding.  This would have involved a tedious radio direction finding homing to the overhead followed by a trombone descent in a safe corridor back to the overhead, hopefully spotting the airfield on the way in.  The controllers were very good at this procedure and it was surprisingly accurate – except it took ages and was no fun at all.

A free descent through solid cloud cover, unless one was certain of the aircraft position could be dangerous - too many airmen in the past had encountered clouds with hard centres for a free descent to be undertaken lightly.  With no navigation aids, as I said, that was seldom an option in the Chipmunk.  But back to heating – not the sun but the mighty power stations.  As I surveyed the brilliant white billiard table top of the stratocumulous cloud, I noted that each of the three coal-burning monsters produced enough heat to cause the cloud above to bubble into a distinctive mound.  The three stations were in a straight line so there was an immediate position line of three distinct bubbles to use in a position calculation. The sun’s azimuth, at its winter elevation, was easy to determine providing further situational evidence.  Finally, there was my mental air plot.  I knew where I had started; I’d flown this way for a little while, that way for a little while longer, generally turned in that area and now, here I was 20 minutes later.  During that time the wind (which I had remembered from the daily met briefing earlier in the day) had pushed me 20 minutes’ worth downwind.  So, all things considered, I was here on my map.  From here on my map to Church Fenton was 5 minutes at 90 knots over there so off we go.

As I approached the overhead I ran through the pre stalling spinning and aerobatiqc checks and for height made a mental note to recover by 1500 feet on the Church Fenton altimeter setting, the cloud base having been about 1700 feet when I climbed out half an hour earlier.  After all these years I cannot recall how much height would be lost in one complete turn of a spin and how much height should be added for the recovery manoeuvre but I calculated the number of turns I need to get down to 1500 feet.  It could have been 4 complete turns at so much per turn plus the recovery and that would have me wings level and back in control by 1500 feet.  Now, simply, throttle closed and slow the aircraft towards the stall and then full rudder (best to the left because the spin characteristics were more stable in this direction) and simultaneously stick fully back.  Hold the full rudder and the stick fully back and check that the aircraft had settled in a spin, particularly the low fluctuating airspeed and the rapid change of direction.  Begin to count the turns.  “Four, Recovering Now!”  Full opposite rudder then stick progressively forward until the spin stops.  Spin stops, centralise controls and pitch to the horizon.  And there it was, Church Fenton spread below.  Change the radio to the Tower and make a joining call for a practice forced landing, “Alpha One Three, High Key to land.”  I gave the engine a brief burst to clear the plugs of any stagnant oil and warm it just in case then continued the engine-off descent to touchdown.  A majestic constant angle of bank, throttle closed, sweeping turn to roll out and kiss the ground on three points right opposite the ATC runway caravan.  All very satisfying but not recommended for trying at home!