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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!
