Can anyone explain this?
Firstly. may I state in advance that I am not an instructor. I know that this forum is not for PPLs to ask for advice, but I hope that you will excuse my posting - perhaps even find it interesting. I just do not know if any other forum would have enough people with the experience in light aircraft to consider this question.
Back in the early 90s when I was a student pilot (about 30 hours total) the flying club organised a fly out to France. I was keen to go and my instructor felt that it would be a good opportunity to do something different.
The weather on the June day saw a warm front lying over the route, with layer cloud forecast from 800 feet to an altitude above the a/c service ceiling, with light rain, zero to light icing etc. Light winds.
My instructor(frozen ATPL) offered me the option of a no go, but said if we did, it would be a very good opportunity to handle the a/c in real IMC and see just how challenging the task was. So off we went.
The outbound leg went very smoothly and so did the return (my instructor checked the weather and it was similar to the o/b forecast)
About 20NM south west of the Dover VOR, some strange things happened very quickly:
1 The groundspeed on the DME went from circa 100kts to 45kts in a few seconds - the airspeed never flickered.
2 Then the airspeed indicator needle fell back against the stops and I would have suspected catastrophic failure if the right wing hadn't dropped as we stalled.
3 My instructor took control instantly and at that point we ran in to very heavy rain - it went very dark, but there was no hail or airframe icing.
4 The VSI then went smoothly against the "up" stop and the altimeter started to increase rapidly.
5 My instructor applied full carb heat and closed the throttle - less noise, no change in the VSI or altimeter.
6 We had another couple of stalls/wing drops and the ASI was all over the place.
7 Strangely enough, the air was not really bumpy, I have rougher rides under CAVOK skies with a bit of wind about.
8 The throttle was then opened fully and the nose pitched down. We were still climbing.
9 Suddenly, we hit a small bump and the VSI and alitmeter reversed. The throttle had to be closed to restrain rapid ASI increase.
10 After about two minutes, we exited the cloud base (layered) indicating 700 feet QNH. On checking in to Manston as we were coming to mid-channel, we were given a QNH which reduced the altimeter reducing to 500 feet.
We arrived back safely and discussed the matter over a couple of pints with the CFI. He had never experienced anything like this himslef and his best guess was that the warm front had produced enough of a lifting effect to spawn a CB, which we had been unlucky enough to get rather too close to.
We did a "forensic" check of the actuals both sides of the channel, but never found any trace of convective activity.
If anyone has an opinion as to what happened and the cause, I would be very grateful as this experience has confused me ever since.
Thanks
[This message has been edited by JamesG (edited 16 November 2000).]