Aircraft: Thorp T-18. Injuries: 1 Fatal. Location: Pahokee, Fla. Aircraft damage: Destroyed.
What reportedly happened: Family members notified authorities when the airplane was overdue. The wreckage was found in pieces along the route of flight the next day.
It was determined that the pilot was operating under visual flight rules while receiving radar traffic advisory service from an air traffic controller. The controller noticed a potential conflict with a Boeing 757 and acted to maintain traffic separation by instructing the 757 pilot to maintain 8,000 feet, asking the Thorp pilot to maintain at or below 7,500 feet, and provided an advisory for wake turbulence.
The Thorp was at 7,800 feet at the time, and the pilot advised that he was descending to comply with the controller’s instructions. When the two aircraft were separated horizontally by about one to two miles, the Thorp pilot reported the 757 in sight.
Radar data indicated that it passed directly beneath the 757, within 500 feet of vertical separation, traveling in roughly the opposite direction.
Investigators determined that although the geometry and the timing of the airplanes passing each other suggest the possibility of a wake turbulence encounter, the Thorp pilot made no comment about encountering turbulence.
Although radar data showed the Thorp turning left as if to get out from under the 757’s flight track, it then turned back to the right and continued climbing on a northwesterly heading for about 2-1/2 minutes until reaching 8,300 feet.
The airplane then turned right and descended to 7,200 feet before it was lost from radar. During the descent, the wings separated from the airplane due to overstress.
The reason for the descent and in-flight overstress of the airplane could not be determined.
The two aircraft were operating in class E airspace, and FAA directives do not require 1,000-feet separation for aircraft in this airspace.
Probable cause: The descent and over-stress of the airplane during the descent, which resulted in the in-flight breakup of the airplane.
NTSB Identification: ERA13FA071
This December 2012 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.
Wake turbulence is a serious issue. And other sources of extreme turbulence can be unexpected too!
Example: late one winter night I was approaching the L.A. basin from the east. It was crystal clear and I was on a very long final from altitude to a straight in at Ontario for fuel, in a Cessna 150.
Is was glassy smooth and I has the speed up, with a nice apporoach set up, perhaps five miles out and about 3,000′ AGL.
Suddenly it was as if a hammer hit me from underneath and everything in the plane hit the ceiling. Then completely smooth again. I was glad I was not wearing a baseball cap with one of those knobs on top! (I always remove them).
No planes anywhere in sight. Ontario did not report any other traffic.
Finally in looking around at the surface I realized I had flown directly over the steel smelters, I believe in Fontana. They must have opened a big blast furnace shortly before I arrived overhead about 3000′ up and caught a very hot bubble of air.
Neither the plane nor I were damaged but it taught me to never be complacent about possible sources of turbulence!
John Thorp designed the Thorp, T-18, to meet aerobatic +6, -3Gs. I think that more than just wake turbulence had to be a factor.
I can understand the thrill of passing close beneath a 757, kind of like buzzing the tower or flying under the golden gate bridge. Impulsive decision, bad idea.
General question for the author/web editor: When will GAN begin using the new URL’s for linking to the NTSB reports? NTSB recently revamped their site and broke everyone’s links from everywhere. (I’ve already pinged their webmaster asking that the old-style URL’s be made functional, but I’m not holding my breath on that one.)
While WT might be a big deal when an airplane is heavy, clean, and slow (see Section 3, AIM) it’s ALWAYS a big deal when the lead airplane is heavier (transport category compared to a light GA). I want at least 5 miles of separation and 1000 feet if I’m in trail and/or crossing below. Very sad that yet again the test is administered to the pilot before the class covered the material. The AIM really understates the seriousness of the problem from enroute WT involving light and ‘larger’ aircraft in 7-3-6 (b) 9.: 9. En route VFR (thousand-foot altitude plus 500 feet). Avoid flight below and behind a large aircraft’s path. If a larger aircraft is observed above on the same track (meeting or overtaking) adjust your position laterally, preferably upwind.
Yikes. We don’t give wake turbulence much thought at altitude.
I guess we need to start.