Under the Overcast

A few weeks ago I got back to my home airport after a long XC flight that got pretty difficult at the end with clouds knitting together into a solid (and lowering) overcast and little remaining sunlight on the ground. And, on getting back I was “rewarded” by the need to jump into a tow plane to aero retrieve 2 guys who landed out at different airports on their way back. Before I left I remarked to a club member that my flight was difficult at the end and that I had ‘” used every trick I knew” to get back. Some time afterward,  that member suggested that it might be helpful to the newer and less experienced XC pilots to explain some of those “tricks” and I agreed to write something up. So, the point of the suggestions below is:  how to get back to your home field when the day deteriorates to large horizontal overdevelopment, cloud spread, and huge ground shadow. Or as my British friends might say,  “What to do when the day goes to poo?”  Here are a few ideas that have worked for me.

Be Patient

Thermals depend on ground heat and the ground stays warm for a very long time after cloud shadow develops. Note that a 2 kt thermal at 4500' AGL left the ground over 20 minutes earlier. Expect that the thermal strength values will diminish as cloud shadow increases but stay optimistic. You will still have time and thermals to get you home! Especially true if you can divert to areas not covered by shadow.

Be Efficient

"Optimistic" doesn't mean pretending that the day hasn't changed. When the day starts to deteriorate you must use all of your altitude efficiently and waste nothing. Forget normal speed to fly settings and use whatever speed covers the most ground most effectively. Downwind this will usually be the best L/D speed. Flying into or crosswind, it will usually be best L/D plus about ½ the wind at your attitude (and note that the wind will change as you get lower). Use all the lift available but do not turn into a thermal unless you feel a genuine surge under the wings and are confident that it is real. It’s OK at normal cruise conditions to make a mistake on the thermal turn direction but when the day is going bad you can’t afford that mistake. You certainly can’t afford a 360 degree turn into nothing or sink.   Keep your eyes outside the aircraft because dust, birds, and other gliders can help a lot. Watch for haze domes and developing cumulus under the overcast.  Fly as smoothly as you can.

Finding Lift when High

When high, go for the dark spots.  As the overcast and spread develop you will usually see dark spots in the overcast (removing sunglasses may help with this). The dark spots are there because the cloud is thickest at that point - usually the result of a residual thermal billowing up in the overcast. You can climb under those dark spots - probably not like you may have been climbing earlier in the day, but we are now in survival mode and will use any climb.

Finding Lift when Low

When low, go for the remaining sunlight. As the cloud shadow develops there will frequently remain a few isolated areas of sunlight on the ground, often quite small. If you are low, go to these (or slightly downwind of them). Just remember to keep a safe landing field in range. The remaining sun-lit patch focuses the thermals at that point and the departing thermal entrains all of the ground heated air from a much larger area than what is sunlit (see the first item above). This trick has saved me many times and once got me a free steak dinner when I radioed this advice to a guy getting ready to land out, “Fly over the sunlight first!” He made a save and bought me supper that night. True story. This really works.

Infrastructure matters

On the day discussed at the beginning of this article it did not surprise me that the 2 guys who landed out did so in fairly high altitude airports located in somewhat isolated areas directly on their course home.  While my flight path home often favors those 2 airports, when the day gets tough I divert east instead to a lower elevation airport I can reach that is slightly off course but surrounded by a large built-up area of urban tenements, industrial buildings, and silos, rail yards and a big steel bridge all to the west (and usually upwind) of the airfield. These features hold heat long after the sunlight stops and I have effectively used that area for a final climb to get home many times.  If low, I arrange my flight path so that I can fly over the built-up area before heading to the airport and I usually find a climb over the infrastructure sufficient to get me home the last few miles, even when nothing else is working.  With a rural or isolated airport as your safety field, you don’t have this tool available.

Lastly, but most importantly, while all of these tricks usually work, you must never depend exclusively on them nor commit to a final glide to your home airport unless you are sure that you can make it and with reasonable margins. Always have an alternate plan and a safety field in your inventory if it doesn’t work. There are few things that take the fun out of soaring (or worse) more than a sketchy final glide over unlandable terrain while watching all of your margins evaporate. Any good land out is better than a failed final glide with no safe options.

Banner photo by Wings & Wheels

 Roy Bourgeois is a well-known US and South African glider pilot who serves as the Chief Pilot for the Greater Boston Soaring Club. He has held several US national records, competed in many US and Canadian Nationals, and has flown over a quarter million XC kilometers in his 4200 hours of gliding. He can be reached at [email protected]