Have you ever had a bad air day where something comes out of left field and smacks you in your unsuspecting face?
It usually starts out innocently enough. The weathers good and your plan is to take a leisurely trip 300 miles down the pike. Youve never really had any problems with the airplane before and nothing looks out of place during the walk-around inspection. Both wings appear to be securely bolted to the fuselage, so in you climb and fire up … so to speak.
Even the tower controllers are in a good mood as they tell you to taxi to runway 13L. What could go wrong? In aviation, anything. But what are the odds something serious could go wrong on the ground in the run-up area? Usually not much, but ask the Piper Dakota pilot whose airplane spontaneously combusted at Des Moines International Airport on a bright autumn day.
Since he walked – ran actually – away unscathed from a flaming pile of avgas and aluminum, some might say he was lucky. Heres what happened based on preliminary investigation.
That Dragging Feeling
The 1979 Piper Dakota had taxied from the FBO to the approach end of runway 13L, a distance of about a mile. Along the way, the pilot noticed that it seemed to take more power than usual to keep rolling, as though something was dragging. Additional power seemed to overcome that unexplained anchor-on-the-tail feeling and the pilot rationalized that the need for more power was due to the increased grade of the taxiway.
Since he couldnt shift into low, he did the next best thing and added more power. That seemed to solve the problem. Seemed to.
Reaching the top of the grade, the dragging problem seemed to miraculously disappear, almost as though whatever had caused the drag had released its grip.
Problem solved. The pilot may have been tempted to utilize that advanced method of problem solving: First recognize the problem, then ignore it hoping it goes away, and when it does, depart quickly before it returns.
No slow learner, he knew he had a problem, so he asked to taxi back to the ramp. Had he done so, he might have noticed bits of what looked like caramelized fiberglass and metal along his taxi route, as though Hansel and Gretel had left scorched bread crumbs to find their way back. Of course, hed have no way of knowing that those ashes were from his Dakota.
Luckily he didnt have a chance to taxi back. Apparently, the dragging feeling the pilot had noted was in fact a brake dragging. When a brake drags long enough it produces prodigious heat. In this case, it produced enough heat to start a fire. Its unclear what burned first, but the tire and the fiberglass wheel pants offered plenty of fuel.
The fire burned through the wheel pants and up the gear leg, which was also shrouded in fiberglass. Flames lapped around the brake lines (full of combustible brake fluid). Its speculative but conceivable that the flames burned through the brake lines, released the hydraulic pressure and, presto, no more drag.
And if that supply wasnt enough, the fuel tank drain valve is located above the wheel pant. Cherokee owners are familiar with the ubiquitous stains on the wheel pants from leaky drain valves. Above the drain valve was the fuel tank. Post-incident investigation showed that the valve in the fuel tank was not leaking. Good thing, too.
Fires are like uninvited in-laws – once they start eating, they dont stop until the food is gone. In this case, the fire bore its way into the left flap, consuming the lower half, then ate away at the lower wing skin aft of the fuel tank. Soon, there was nothing left of the entire panel aft of the tank.
Yes, aluminum burns. That may not be the correct technical term, but fire consumed the aluminum skin of that left wing like so much waxed paper on a barbecue grill. It burned ribs, it burned the aileron, it burned and burned then burned some more. Amazingly – and who says the gods dont watch over fools and pilots? – it didnt torch the fuel tank.
The flames did, however, lap at the trailing edge of the tank, leaving soot on the fuel quantity sender. No doubt, given a little more time, this incident would have been horribly tragic.
For much of the roast, the pilot was unaware of the conflagration beneath his left fuel tank. Cant fault him for that; wings dont normally burst into flames during a run-up. Theres no spot on the checklist for: Lower Flaps; Verify Not In Flames. A nearby pilot, however, found it curious and asked tower to please relay a message to the Dakota pilot: Get out!
He did. And someone dialed 9-1-1. Its now up to the owner to call Piper and order a new left wing. Chances are they wont have many in stock. And if they did, chances are even better it wont be cheap. Now, thats what I call a bad air day.
Also With This Article
Click here to view “Routine Arrival? Yeah, Right.”
-by Paul Berge
Paul Berge is editor of Aviation Safetys sister publication, IFR.