NTSB Factual Report

On January 10, 2002, at 1042 eastern standard time, a Harold L. Springer Longbow 150 experimental airplane, N150LB, registered to a partnership and operated by the pilot, collided with the ground while maneuvering in Oak Hill, Florida. The personal flight was conducted under the provisions of Title 14 CFR Part 91 with no flight plan filed. Visual meteorological conditions prevailed at the time of the accident. The airplane sustained substantial damage, and the private pilot received fatal injuries. The local flight departed Space Coast Regional Airport in Titusville, Florida, at 1000.

According to a friend of the pilot, the pilot radioed on a common frequency after takeoff to report that flight conditions were favorable. About 40 minutes later, a witness on the ground in Oak Hill, Florida, observed the airplane fly overhead in circling maneuver, then dive vertically into the ground. The witness stated the airplane's engine was audible.

Examination of the accident site revealed the airplane collided into a lagoon in a nose-down attitude and flipped inverted. Flight control surfaces were found intact and attached to their respective cockpit controls, and fuel was observed in the tank.

An autopsy was performed on the pilot by the Office of the Medical Examiner, Volusia and Seminole Counties, Daytona Beach, Florida. The cause of death was listed as blunt force injuries. Forensic toxicology was performed on specimens from the pilot by the Federal Aviation Administration Toxicology and Accident Research Laboratory, Mike Monroney Aeronautical Center, Oklahoma City, Oklahoma. The toxicology revealed 31 percent carbon monoxide was detected in the blood, and diltiazem was present in the blood and in the liver. Diltiazem is a prescription drug in a class called calcium channel blockers, commonly used to treat patients with cardiovascular disease. The pilot had a history of atherosclerotic cardiovascular disease.

The airplane was built by the pilot and was his third completed project. Records and receipts provided by the co-owner revealed the airframe had been built from a 1961 Piper PA-22-108. The Lycoming O-320 engine and the PA-22 exhaust system had been purchased separately from an aircraft salvage facility in 1997. The engine received a zero-time overhaul in 1997, and the co-owner estimated the total time on the engine when the accident occurred was 23 hours. The airplane was equipped with a cabin heat system in which the heat was provided by a heater muff attached to the exhaust system. Ventilation for the cabin was provided by a controllable air scoop and a window vent on the left side.

Metallurgical examination of the exhaust muffler and heat exchanger assembly was performed by the National Transportation Safety Board, Office of Research and Engineering, Materials Laboratory Division in Washington, D.C. Examination revealed three stainless steel standoff rings were discontinuously welded to the outside of the stainless steel muffler canister, providing a space of approximately 0.5 inch between the muffler and aluminum heat exchanger shroud. The center standoff ring appeared to separate the heat exchanger into two separate chambers. This barrier between the two chambers was not airtight.

The heat exchanger shroud contained five ports. The muffler exhaust pipe passed through the shroud at one port, which was a slightly irregular opening approximately 2.5 inches in diameter; the gap around the exhaust pipe at the port was approximately 0.4 inch. Two ports were located on the same side of the heat exchanger as the exhaust; one port was completely covered by a riveted patch, and the other port had a riveted tube attachment fitting. The two other ports had riveted tube attachment fittings and were located at the other side of the heat exchanger. One of these fittings had a piece of rubberized fabric tube attached with a hose clamp.

The wall of the muffler canister was fractured through in the area where the exhaust pipe was welded to the stainless steel muffler canister. The fracture surfaces observed along planes nearly perpendicular to the muffler wall were darkly colored by corrosion. This type of fracture surface was observed at the edge of the weld bead around the exhaust port over a circumference of approximately 180 degrees, and along several cracks branching outward from the weld bead propagating axially approximately 0.5 inches. The fracture surfaces observed along planes at a 45-degree angle to the muffler wall displayed no corrosion. This type of fracture surface branched out circumferentially approximately one to two inches from the corroded fracture surfaces on either end of the exhaust outlet.

A review of Federal Aviation Administration Advisory Circular AC65-12A revealed in Chapter 2, Induction and Exhaust Systems, Exhaust System Repairs: "It is generally recommended that exhaust stacks, mufflers, tailpipes, etc., be replaced with new or reconditioned components rather than repaired. Welded repairs to exhaust systems are complicated by the difficulty of accurately identifying the base metal so that the proper repair materials can be selected. Changes in composition and grain structure of the original base metal further complicate the repair.... Weld beads which protrude internally are not acceptable as they cause local hot spots."

NTSB Probable Cause

The improper modification of the exhaust muffler which resulted in fractures that enabled the contamination of the cabin heating and ventilation system. The pilot subsequently became incapacitated by carbon monoxide poisoning, and the airplane descended uncontrolled into terrain.