N18994Beech C23 · 1977

On September 23, 2023, about 1914 central daylight time, a Beech C23 airplane, N18994, was substantially damaged when it was involved in an accident near Gonzales, Texas. The pilot received minor injuries. The airplane was operated as a Title 14 Code of Federal Regulations (CFR) Part 91 personal flight.

According to the pilot, he intended to complete a personal flight to Roger M Dreyer Memorial Airport (T20), Gonzales, Texas. During the final approach to runway 15 he experienced wind shear and elected to go around. He applied full throttle and began to climb out when the engine sustained a loss of power, so he made a forced landing to a field off the left side of the runway. The airplane collided with a fence and a tree, which separated the right wing near the wing root.

Postaccident examination of the airplane revealed substantial damage to the wings and fuselage. The undamaged exhaust system was examined using a flashlight in the tailpipe and a lighted borescope, which revealed a blockage in the tailpipe; the muffler was then removed and cut open. The flame tube was blocking at least 95% of the tailpipe exit path; the piece was lodged in the tailpipe. The fracture area appeared degraded and covered in corrosion. A 3-inch crack was noted on the muffler endcap opposite of the separated flame tube. There were no other mechanical malfunctions or failures that would have precluded normal operation.

The airplane maintenance logbooks revealed that, during a maintenance inspection on December 24, 1997 (3,523.42 hours total time and 1,260.42 hours since major overhaul), the exhaust system was inspected “for leaks and cracks. System found to be satisfactory.”

On January 2, 1999 (3,556.5 hours total time and 1,293.50 hours since major overhaul), another maintenance inspection was conducted by the same mechanic and there was no mention of the exhaust system.

On March 21, 2000, the airplane’s muffler was repaired and inspected by a separate exhaust system repair station. The work order for this muffler repair revealed that the muffler was to be inspected and repaired. The items replaced included: 3 tabs, the outer shell, 2 caps, 2 flame tubes, 2 elbows, 2 beaded ends, 2 end plates, and the tailpipe.

On April 1, 2000 (3,603.36 hours total time and 1,340.36 hours since major overhaul), another maintenance inspection was conducted by the same mechanic from 1997 and 1999, when they reinstalled the repaired muffler.

There were no additional maintenance logbook entries found specifically related to a muffler repair or replacement.

The most recent 100-hour/annual inspection was completed on November 23, 2022, (4,052.8 hours total time and 1,789.8 hours since major overhaul), during which 8 exhaust clamps were replaced and a new exhaust stud was installed on the No. 4 cylinder. There was no specific mention of the muffler; however, 14 CFR Part 43 Appendix D—Scope and Detail of Items (as Applicable to the Particular Aircraft) To Be Included in Annual and 100-Hour Inspections, states in part:

(d) Each person performing an annual or 100-hour inspection shall inspect (where applicable) components of the engine and nacelle group as follows:

(8) Exhaust stacks—for cracks, defects, and improper attachment.

The installed Dynon Avionics revealed that the airplane total time was 4,108.2 hours at the time of the accident. Therefore, the muffler had been installed on the airplane for 504.84 hours.

Beech maintenance and overhaul documents revealed that the exhaust system should be overhauled or replaced every 800 hours or when the condition warrants replacement. The exhaust muffler and shroud should be inspected every 100 hours. The documentation states, “It is recommended that at each 100 hour and/or annual inspection, all exhaust muffler shrouds be removed and the muffler thoroughly inspected for cracks, leaks and (if applicable) deterioration of the internal tubes which could cause a decrease in engine power due to blockage of the exhaust.

According to the Federal Aviation Administration (FAA) FAA-H-8083-32B, Aviation Maintenance Technician Handbook – Powerplant:

Internal Muffler Failures

Internal failures (baffles, diffusers, etc.) can cause partial or complete engine power loss by restricting the flow of the exhaust gases. If pieces of the internal baffling breaks loose and partially or totally blocks the flow of exhaust gases, engine failure can occur. As opposed to other failures, erosion and carburization caused by the extreme thermal conditions are the primary causes of internal failures. Engine backfiring and combustion of unburned fuel within the exhaust system are probable contributing factors. In addition, local hot-spot areas caused by uneven exhaust gas flow can result in burning, bulging, or rupture of the outer muffler wall.

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. However, when welded repairs are necessary, the original contours should be retained; the exhaust system alignment must not be warped or otherwise affected. Repairs or sloppy weld beads that protrude internally are not acceptable as they cause local hot spots and may restrict exhaust gas flow.

FAA Advisory Circular (AC) 91-59A, "Inspection and Care of General Aviation Aircraft Exhaust Systems," emphasizes "the safety hazards of poorly maintained aircraft exhaust systems (reciprocating powerplants) and highlights points at which exhaust system failures occur. Further, it provides information on the kinds of problems to be expected and recommends pilots perform ongoing preventive maintenance and mechanics perform maintenance." The AC also notes that potential failures can include partial or full engine power loss caused by loose baffles, cones, or diffusers on mufflers and heat exchangers that partially or completely block the exhaust gas outlet flow.