There isnt a pilot out there who doesnt harbor a flying fantasy of some sort. Some dream of bouncing around the country in a J-3 Cub. Others want to fly the biggest jet or the hottest stunt plane or fly every kind of aircraft that can still stretch the chains of gravity.
For a relatively large number, nothing gets the blood pumping like the prospect of manhandling a warbird through tortured paces, drawing a bead on some unlucky prey like the ultimate computer game come to life. It is for these people that an entire segment of the aviation industry was born.
Fighter fantasy flights have been offered in various locations around the country for years. Usually staffed by ex-fighter pilots, the companies deck the aspiring Top Gun out in a flight suit, complete with patch. They brief the customer on various dogfighting tactics and maneuvers, and then strap the neophyte into the seat of an ersatz fighter.
The airplanes of choice for the role tend to be aerobatic 2-seat tandems with relatively high performance. Theyre typically fitted with gun sights and lasers. The most elaborate will trail smoke when hit by a pursuer.
Siai Marchettis have been put into service, as have Extra 300s, but the most popular airplane is the T-34 Mentor, a military trainer built by Beech from 1953 to 1958. The T-34 filled the role as primary trainer while having enough performance to prepare fledgling pilots for more capable aircraft down the line.
One spring morning, a recently retired airline captain walked into the office of a combat simulation company in the suburbs of Atlanta. Less than a year earlier the pilot had run smack into the FAAs age 60 rule and made his last flight in an airliner. His Class 1 medical expired.
For the combat simulation flight, he was paired with a 15,000-hour former fighter pilot who had over 450 hours in the T-34. For the purposes of the flight, the employee was considered the pilot in command, with the customer considered the second pilot.
After a preflight briefing, two company T-34As took off at noon and flew to a special patch of airspace near Rydal, Ga., where the company and the FAA agreed the combat simulations could take place.
The Mentor was equipped with three video cameras and a VHS recorder, which were used to record the flight to make a souvenir tape for the customer. The companys practice was to familiarize the customers with the combat maneuvers, then have the customers dogfight each other.
Flights were typically planned that the maneuvers would not pull more than 3 to 4 gs, but the operator permitted maneuvers up to the original certification of 6 gs. One of the other airplanes owned by this operator reportedly experienced 12 gs during one mission.
The flight was about 30 minutes old when, during a dogfight the retired airline pilot won, the company pilot repeatedly urged the customer to pull harder on the stick during a maneuver called a pitchback. The pitchback is a climbing 180-degree turn with 40 to 50 degrees of bank.
After that engagement, the two pilots were discussing the maneuver, talking about using the rudder aggressively to bring the nose in line with the target. At one point in the discussion, the company pilot said, We had 4, almost 5 gs there. So you got … you had good performance around the turn.
The two airplanes then set up for another engagement, and a couple of minutes later, the customer lost a dogfight because during one turn he did not pull the nose aggressively enough. After the maneuver, the company pilot stressed getting the nose high.
Way up here, he said, demonstrating the maneuver. Well get it way up there then youll be able to get one, uh, keep him in sight but two, reduce your rate of turn, uh, radius of turn.
The airplanes then set up for what would be their final engagement. The Mentor climbed to 8,000 feet and the target airplane would be coming head-on at 7,000 feet from beyond visual range.
The employee pilot said he would keep the power up after the climb to 8,000 to pick up some speed. A few seconds later, the customer spotted the target, low and off to the left. As the customer began to dive, the employee pilot said, There you go. Roll all the way through. Harder. Harder. Harder. All the way through. Thats it. Thats right, bury your nose. Bring it on down. Thats it. Good.
The video recorder picked up the sound of increasing wind noise and the employee muttered [Expletive] hot, followed in a few seconds by, OK, now dont chase him into the ground.
As the words come out of his mouth, a bang is heard on the recording, along with the company pilot in the other airplane saying Bail out! Bail out! Bail out!
The T-34 plummeted to the ground, its right wing gone. Despite the altitude, neither pilot used his parachute. Both were killed in the accident.
Although the NTSB report does not mention it, other reports surfaced among the warbird community that the wings separation was not instant, that it remained attached briefly, perhaps by control cables, and flapped against the canopy several times before ripping free. That possibility brings up the notion that perhaps the pilots were casualties even before the airplane hit the ground.
Several witnesses, including the other company pilot, saw the ruined airplane spiraling to the ground. None reported any activity that resembled an attempt to bail out.
When the wreckage was examined, the right wing was found more than a mile from the main wreckage. The rear spar had failed in at least two places. The forward spar had separated at the wing fitting area, where the wing attaches to the fuselage.
The airplane had accumulated 8,354 hours total time at the time of its annual inspection six weeks before the accident. Since the combat simulation company bought it in 1990, it had accumulated about 4,000 hours in the arduous duty of letting people live out a flying fantasy. About 200 hours were logged by a private owner who had the airplane for more than 20 years, meaning the airframe had logged more than 4,000 hours doing military training operations.
When NTSB metallurgists looked at the wing structure, they found a number of spots where the complex spar assembly was showing signs of fatigue. They examined the spar from the left wing, which had not separated in flight and found similar fatigue signatures in similar places.
The NTSB then looked at a wing assembly that had been removed from another company T-34 three years earlier after cracks were discovered in the lower spar structure of the right wing. Using an electron microscope, metallurgists were able to determine there were two spots where cracks apparently caused by overstress had propagated. Several other spots showed signs of fatigue, both when examined by eddy current and when examined under an electron microscope.
The fact that only the fatigue on the lower cap of the aft spar on the right wing progresses a large distance indicates that most of the cracking originated relatively recently, the NTSB concluded in a safety recommendation to the FAA shortly after the crash.
Another air combat company flying T-34s had detected a crack in the left wings aft spar cap a few weeks before this accident, but discarded the parts before the crash and they were not examined by metallurgists.
The NTSB found one other incident of wing structure cracking in T-34s, in a Venezuelan aerobatic airplane. The boards safety recommendation said, Although typical wing loading spectra generated by training missions, aerobatics and air combat simulation flights are not available, the Safety Board believes that air combat simulation flights may induce a larger number of high-positive wing loading events per flight than other operations. In addition, the multiple initiation sites and large number of fatigue cracks in the wing structure suggest that the fatigue damage is both recent and related to high stress.
The Quick Conclusion
Without examining any airplanes that had not been used for air combat simulation, the board concluded it is likely that the damage came from the mock dogfighting.
In fact, the NTSBs conclusion omitted some of the evidence available in the last few minutes of the flight.
The employee pilot had said he was going to keep the power up to build speed after the climb. Shortly thereafter, analysts noted the sound of increasing wind noise, suggesting that the airplane was flying fast as it began its final maneuver – perhaps much faster than Va of 148 knots and perhaps faster than 200 knots.
While it seems the videotape may provide other clues as to the speed and orientation of the aircraft, a specialist retained by the NTSB during the investigation declined to make such an analysis. He cited three primary reasons why any data derived would be questionable.
The altitude would allow atmospheric refraction to distort any measurements of where the airplane was over the ground.
The low resolution of the videotape and the wide angle lenses would make it difficult to determine where the airplane was.
And the original lenses used to record the image would have to be obtained and calibrated, due to the large variation in the manufacturing quality of such lenses.
While an analysis is possible, the factors listed above would make the accuracy of the results questionable, he told the NTSB.
However, the voice transcripts and the general nature of the maneuvers involved points out that the airplane could very well have been overstressed regardless of any pre-existing fatigue. When describing both the pitchback and the sliceback, the operators manual specifically warns, Caution: When starting a pitchback/sliceback at high energy levels, an overly aggressive pull could result in an over-G.
Recall that two maneuvers before the failure the employee pilot had told the customer to pull harder, then adding they had pulled nearly 5 gs. In the next maneuver, the customer didnt raise the nose high enough and was shot down. After that, the employee pilot demonstrated the maneuver again, pointing out again how a harder pull was needed to tighten the turn radius.
Those two lessons could have been learned well. Even though the next maneuver was a descending turnaround instead of a climbing turnaround, it requires a positive pull because the airplane is banked to 125-145 degrees. However, pulling gs and rolling simultaneously induces added g-forces to the wings due to asymmetric wing loading.
In a left turn, as the accident airplane was at the time of failure, the aileron on the right wing is deflected down, forcing the wing up and in effect imposing more of a load factor on the wing than is registered on the accelerometer in the cockpit. Even an F-15 can pull only 2.5 gs in pitch and simultaneously sustain full aileron deflection.
In the case of the T-34, the added lift from the point of the aileron would put extra stress on the aft wing spar, which did fail in two places. Once the aft spar failed, the wing would twist and the forward spar would quickly follow.
The recommended speed of entry for the sliceback is 120 knots – a speed the airplane almost certainly was exceeding because of the evidence of increasing wind noise heard on the tape. Even if the airplane was flying at Va, which it was probably exceeding by the time the wing failed, the pilot could only have made a full aileron deflection or a full pull on the stick, not both.
In the aftermath of the crash, the FAA and Raytheon put flight limitations on the airplanes and designed an expensive, intrusive series of tests to assess the condition of the wing structures. However, without having examined a wing exposed to 50 years of only normal T-34 flying, the conclusion that accelerated fatigue was caused by dogfighting and then caused the crash is suspect.
In such an extreme pursuit as mock combat, civilian fliers can learn what military pilots have known for nearly 100 years – that any aircraft can be overstressed if the pilot loses sight of its limitations.
-by Ken Ibold
