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Trapped above the overcast cloud layer in glider
The flight took place in south of France in June 1996. Despite the spring coming and the atmosphere warming up day after days, a regular mistral (a north wind often blowing in the Rhône valley) was generating very good mountains waves around the airfield. As I was rather expecting some thermal conditions, I arrived a bit late in the flying club to profit of the wind laminar flow prevailing early in the morning. As a matter of fact, the majority of the gliders fleet is already airborne. Hopefully, there is still a sailplane parked near the hanger. Searching for other club members to position the glider on the runway, I find a friend also very motivated to fly. That’s very fortunate as the sailplane which is still available is a two-seater. We soon prepare the machine for a dual flight and also find a tug pilot ready to tow us. As can be imagined, this good conjunction of events makes me very excited. Moreover, we are 2 young fellows around 20; I just logged my 100th hours on my logbook but my friend is largely more experienced. The relief reaching 2,400 feet ASL just 7.5 Nm North-West from the airfield actually generates strong thermodynamic lifts and, after releasing the rope around 2,700 feet ASL, we quickly raise altitude. After fighting in the turbulences, the airflow organizes in laminar waves near 3,500 feet and we can enjoy very calm conditions, with a positive variometer around 3 m/s (~600 ft/min) and a ground speed close to 0. This sort of feeling of “calm out of chaos” well known by soaring pilots can be a contributing factor for the crew to release vigilance. Actually, a reason why such conditions have been encountered so late in the season, whereas the sun heat should have disorganized the mountain waves system, might be the very humid air mass. Indeed, we have observed a lot of rotor clouds in the lower atmosphere level and a Foehn window is eventually quickly materializing below us. But for the time being, our intention is drawn by others matters: we try to optimize our climbing rate and route as it is pretty late to start a cross-country flight. We spot a single-seater Discus from another gliding site heading north, approximately 2,500 ft higher than us. On the radio, the pilot tells that he rose to an altitude of more than 13,000 ft, and that makes me totally ‘pumped’. And yet, I can feel that my colleague in the rear seat (again, he has a lot more experience than I have) is not such enthusiastic, as he draws my attention on the Foehn window which is narrowing. The Discus with better performances and extra altitude, can aim at another window in the clouds about 12 Nm North of our position, but not us. Soon, a message from the ground starter also warns the nebulosity around the airfield tends to turn to broken at medium altitude. We then decide to leave the wave lift and push the stick forward near the VNO. But it does not appear to be sufficient now: even with a negative vertical speed and quickly losing altitude, it becomes soon obvious that we are going to lose our race against the cloud layer “soldering”. We navigate in order to fly where the cloud thickness is the less important, and we manage to keep the ground in view through the nebulosity in some spots. But it has become obvious we have no other choice than to perform a breakthrough in the clouds. Needless to say, the glider has no valid horizon indicator, and even less any kind of IFR instrument. Nearing the upper base of the clouds, we see a road and flat landscape through a hole in the nearly overcast cover and decide to begin the descent there. We apply the method we were taught at that time as per the glider pilot curse: indicated speed ~110km/h (~60kt), bank angle to 30°, airbrakes fully deployed and elevator trim set up. In that configuration, the glider is stable hands off the stick (that prevents bad pilot input due to disorientation in absence of external visual references), with a high sink rate. Moreover, the inclination also limits the range of our evolution, which is also a problem when you are “blind”, particularly in a mountain region.... Our sailplane enters in the “woolly mattress” at 1200 m (~4000 ft), with -4 m/s at the vertical speed indicator. There is no GPS on-board, but we are confident to be far from the relief, nevertheless I feel rather uncomfortable. The cover is not homogenous and we can sometimes briefly see the horizon that, albeit dazzle, confirms the bank and pitch attitude are steady. We finally emerge out of the clouds at around 900 m (~3000 ft), with the relief still below and south of our position We then take the direction of the airfield and t;lhe rest of the flight and the landing were uneventful.
Lessons learned:
- Even when the sky is clear all around, the clouds can form a barrier between you and the ground. Of course, in a powered aircraft, it might be possible to continue in “VFR on the top”. But still, in harsh windy conditions, with a low-powered aircraft, flying to find a window in an overcast layer can be iffy.
- We were never more than 30 continuous seconds in IMC (as we were able to see from time to time the horizon) ... but I can witness for other pilots it seems very long!
- The procedure we applied seems to be however correct, and particularly, refraining to touch the control once the glider was in a steady position.
- To be careful about mutual enthusiasm of a dual crew.
21rst Nov. 2020 update, with this very remarkable YouTube video of a ridge flight that almost turned to a catastrophic accident .
4 min of flight is long to watch on YouTube, and very easy to judge abruptly; but it is very short when you are on control. The first part is normal cloud / ridge, until the crew turn left (~ 1min40), searching for the best climb rate, instead of remaining with clear sky on the right.... and even more , by heading 30° to the left, they come closer to the hill while the visibility is starting to be poor. At 2 min, they should have turned right without delay, but the crew seems to be monopolized by the high sink rate (down to -8m/s) that brings them to the cloud mass and worsen the visibility. There is apparently a lack of hill proximity awareness. At 2 min 50, they regain ground visibility to the right; although it is still very hazy, the height seems already very small! 5 sec later, they are at a few dozen meters from the ground , and the collision avoiding manœuvre briefly bring them to +8g... which of course put them back in the clouds. The camera falls in the cockpit but we can see they state IMC close to the hill, being close to spin (3 min 41) before recovering ground visibility and control.
Thank to the pilots who have posted this video, it’s courageous. I wish them to be more careful in the future and a lot of nice and safe flights. Also I hope this sharing will serve for education of glider pilots to show the danger of losing ground sight, even momentarily.
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Glider IMC, Manawatu New Zealand
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