During the hot summer months it’s not unusual to start the day crystal clear, have a few puffys float around, and then by mid afternoon you have a rain shower move through. One such summer in the midwest I had been keeping an eye on a building cumulus cloud. It pretty much stayed stationary the whole day. I wondered if we would be effected by it. I continued to drop loads as it was stationary about 10 miles west of the airport. Climbing for altitude was not hindered at all. However, after watching this cell build for about two hours it did seem to start to move towards the dropzone. I loaded up another load in the Twin Otter and began climbing for 14K msl.
The jumprun was to the south and the cell was visible out my right front window. The Twin Otter has lots of windows for skydivers to see out themselves. I pointed out the cell to the tandem masters on board. I even called down to manifest to see if the wind was picking up. The report was all looked good. I made my call to center and on local frequency of the impending drop. All looked good still from 14k for a clear drop to the ground. I gave the red light for door open and green light to begin the drop. All the jumpers left and I began descending to the south and making a big box around back to the base leg for runway 23. As I entered the base I saw all the canopies open facing west and holding. They were not driving into the wind at all. I looked to the west and the sky was very dark with a rain shaft coming down still west of the field. I thought “Ok we’ll be done for awhile while this passes.” Then I saw a bolt of lightning come out of the bottom of the cloud. I began to feel very unnerved for those still under canopy and exposed to these elements. I had dropped them into bad situation. As I rolled on to final I saw canopies turning and running to the east. They had begun to back up under canopy. The dropzone was bordered by a river with a deep ravine. If you did not bail out early and head east you might not make it across the river and landing in the river ravine could be very turbulent. I saw some canopies of experienced jumpers on the ground. I saw people jumping on one tandem pair that had exited early and gotten down before this gusty outflow had hit. But others still in the air were now faced east and looked like they had lit afterburners on jet engines with the speed they were traveling over the ground. I knew they would make it across but didn’t know how their landing would go facing back into the wind.
The final approach had been stable in smooth air. And just as I was about to touch down I saw bits of crops now blowing across the runway. I had many clues that should have told me to go around and wait out the storm. But I thought I still had a clear shot. To those who have flown the Twin Otter you will know that it has a HUGE vertical fin with a big rudder. It gives excellent directional control. However, it’s a HUGE fin that likes to weather vane you and I got hit with a 30 mph wind just as I touched down. After dropping jumpers the aircraft is very light and floaty. I pull full aileron into the wind and darn near full opposite rudder but the gust was too much and weather vaned right into the wind. I exited the runway and ran over some bean crops. Fortunately a north-south grass runway kept the crops from being too long in my path. I exited the crops onto the grass strip and made a left back over the paved runway towards the ramp and hangar. The other Twin Otter was already mostly in the hangar as I came pulling up. We got it in the hangar just before the skies opened up with rain and the doors were quickly closed. I got out and saw I had dragged some green vines with me. Another jumper noted the stowaways with a raised eyebrow.
Fortunately, there were no serious injuries from the landings but one tandem master fractured and ankle during his landing on the east side of the river. I have always felt very bad about this as skydivers trusted me to only drop them in acceptable weather conditions. I was perfectly legal in my drop with cloud clearances. The wind at the time of the drop was well with in good jumping limits. But it went bad in a hurry.
I learned a bit about how to communicate better with my manifest people. I needed to ask them specific questions (Do you see any rain or lightning coming out of that cloud to the west?) My query about how the winds were fell short of getting a clear picture of the conditions on the ground. Also I needed to make better considerations when coming in to land. There were several visual cues that told me this landing would be dicey. I didn’t bend any metal but a good pilot uses his good judgment to avoid using his good skills.
Nowadays we have pretty good and free weather radar websites. If you have someone in manifest that can glance at it once in awhile for you and adequately communicate anything developing it’ll be a plus. But when in doubt shut the plane down and go inside to check it yourself. Use all the tools at your disposal.