NTSB Factual Report

HISTORY OF FLIGHT

On April 19, 2005, at 1823 Pacific daylight time, a Beech 35-C33A, N299X, experienced a loss of engine power and collided with terrain during a forced landing at Paso Robles, California. The airplane was operated by Squadron Two at Reid-Hillview of Santa Clara County Airport, San Jose, California, as a rental airplane under the provisions of 14 CFR Part 91. The commercial pilot and passenger were seriously injured, and the airplane sustained substantial damage. Visual meteorological conditions prevailed, and a visual flight rules flight plan had been filed. The flight originated at Van Nuys, California, at 1730.

The pilot stated in the Pilot/Operator Accident Report that about 5 miles west of the Avenal VOR, cruising at 8,500 feet mean sea level (msl), he heard a loud noise and the engine started running rough. The pilot checked the oil temperature and pressure and noted that they were normal in the green arc. He reduced power to 16 inches of manifold pressure, and noticed that the airplane was not maintaining level flight. He contacted Oakland center and started to divert to Paso Robles. At this time there was another loud bang from the engine compartment; the engine rpm dropped dramatically, and the cockpit started to fill with white smoke. The pilot made a mayday call and Oakland center gave him vectors to the Paso Robles Airport. He established an 80-knot glide and set the power at 13 inches of manifold pressure (1,500 rpm). The smoke cleared from the cockpit, and he determined he was within gliding distance of the airport when the engine cowling popped open and stayed open. The increased drag from the cowling increased his rate of decent to greater than 800 feet per minute; he realized he now would not make the airport and set up for an off field emergency landing into what he thought was a green farm field but turned out to be a vineyard. He lowered his landing gear and approached the vineyard at 45 degrees to the rows. He had started the landing at 75 knots when the left main landing gear snagged a grapevine row pole and wires. The plane veered to the left, and stopped almost immediately. He recalls that his head hit the dashboard during the landing and the passenger in the right seat was unconscious after the landing.

AIRCRAFT INFORMATION

The airplane was a Beech Debonair C33A, serial number CE-37. Review of the airplane logbooks revealed a total airframe time of 6,083.1 hours as of March 4, 2005. The tachometer time read 0186.2 after the accident, which corresponds to a total time of 6,106.8 hours at the time of the accident. The last 100-hour inspection was performed on September 28, 2004, at 6,018.7 hours, and a 50-hour inspection was performed on January 31, 2005, at 6,068.2 hours.

The engine was a Continental IO-550-CCB, serial number 676637. The engine logbook recorded a total time (TT) of 2,770.9 hours and 1,673.6 hours since maintenance overhaul (SMOH) as of the last oil change on January 31, 2005. The total time accrued on the engine at the time of the accident was 2,809.5 hours. An engine logbook entry dated September 28, 2004, (1,624.1 hours SMOH) corresponds to an airframe logbook entry of the same date annotating the compliance of a 100-hour inspection and records an oil change, oil filter exam, compression check, gapped spark plugs, checked magneto timing, and a leak check. This engine logbook entry is consistent with a 100-hour engine inspection.

This airplane was equipped with lap belts for the occupants but not shoulder harnesses or shoulder straps.

WRECKAGE AND IMPACT INFORMATION

The San Luis Obispo County Sheriff's report described the airplane as being in a vineyard facing south when they arrived on scene. The landing gear was down and it appeared that it may have hooked the onto the grapevine tension wires. There seemed to be little or no skidding with the plane having stopped on impact.

Examination of the on scene photographs by the National Transportation Safety Board Investigator depicts the airplane in about a 10-degree nose down attitude in the vineyard. The engine was displaced downward about 25 degrees with the pivot point of rotation at the bottom center of the engine firewall. The left wing root trailing edge was peeled up from the inside corner towards the middle of the wing, exposing the left landing gear structure. There appeared to be no buckling of the cockpit cabin area structure and the windscreen was in one piece affixed to the airframe. The seats remained attached to their respective seat rails. The propeller was detached from the engine crankshaft flange.

SURVIVAL ASPECTS

To estimate the landing forces that the occupants would have experienced the following calculation utilizes the "Quick Look Analysis" technique as described in NTSB/SR-83/01. The pilot reported a landing airspeed of 75 knots. The sheriff's report stated that the airplane left little evidence of a ground scar and appeared to have stopped on impact; therefore, it was assumed that the airplane stopped in a distance equal to its own length, 7.8 meters. The shallow angle of impact indicated that the majority of the decelerating forces would have acted along the airplanes' longitudinal axis. Using these values the approximate force that the occupants would have experienced was a peak impulse of around 19.5 g's over a pulse time period of about 1.4 seconds.

The Beech 35-C33A was certificated under the Civil Aeronautics Regulation (CAR) 3. CAR 3 paragraph 3.386, Emergency Provisions, dictates that the fuselage shall be designed to give reasonable assurance that each occupant, if he makes proper use of belts or harness for which provisions are made in the design, will not suffer serious injury during minor crash conditions as a result of contact of any vulnerable part of his body with any penetrating or relatively solid object given an assumed forward deceleration of 9 g's.

There was no observed failure of the lap restraint system or of the seats in this airplane. The main aspect of the occupant restraint design was the presence of a lap belt restraint system but no upper body (shoulder harness/strap) restraints. This restraint system conforms with the type certificate for this airplane, which is less restrictive than the current regulations due to the age of the design. A supplemental type certificate (STC), SA1583GL, for the addition of shoulder harnesses to this model of airplane is available.

Both occupants received serious head injuries.

TESTS AND RESEARCH

Engine Examination

On May 5, 2005, the airframe and engine was examined at Aircraft Recovery Services, Pearblossom, California. The examination was performed by the Safety Board investigator-in-charge (IIC) and a technical representative from Teledyne Continental Motors.

The engine was a Continental IO-550-CcB, serial number 676637. Examination of the engine logbook revealed that the engine was overhauled on July 15, 1999, and installed into N299X on August 11, 1999. The last annual inspection was performed on June 21, 2004, at an engine total time since maintenance overhaul (TTSMO) of 1,463.5 hours. The engine logbook entry for the annual inspection included the following entry: "Four cylinders removed (#2, 4, 5 & 6) for overhaul. Installed 4 each customer supplied cylinders, repaired by Gil's Engines, reassembled engine, baffles, intakes, exhaust, ect. torqued cylinder, finished engine. Engine run up and ops checked okay." The TTSMO on the engine at the time of the accident was 1,653.0 hours.

Examination of the engine revealed a 3-inch by 7-inch hole in the top of the crankcase that extended past the crankcase parting line and into the engine data plate pad that was aligned with the connecting rod above the number 4-cylinder position. The number 4 cylinder and piston were not present on the engine. The number 4 connecting rod and cylinder attaching hardware were recovered from the inside bottom of the engine cowling. Examination of the number 4 cylinder mounting pad revealed that the bottom two cylinder hold down studs at the 5 o'clock and 7 o'clock positions were fractured about mid thread line, extending above the case 0.369 and 0.406 inches, respectively. The cylinder hold down studs at the 2 and 3 o'clock (seventh stud) position were intact with very little damage. The 4 o'clock stud had slight smearing of its last three threads. The 10 and 8 o'clock through bolts were fractured flush with the engine case. The 9 o'clock seventh stud was not present, but the number 2 cylinder base flange on the right side had rub marks consistent with fretting adjacent to the seventh stud location. There was dark discoloration of the cylinder pad surface consistent with fretting at the 3 and 9 o'clock positions.

Fastener items collected from the inside the engine cowling were: the fractured ends of both number 4 cylinder bottom cylinder studs with flat bottomed nuts present; one complete top cylinder stud without nut; both number 2 and 3 cylinders left seventh stud plates; the fractured end of the number 3 bottom through bolt with nut present; the left number 3 seventh stud with conical nut present and aluminum metal in the crankcase end threads; one 3/8-inch cylinder hold down nut (flat bottom flange); and one 5/16 inch bolt with aluminum present in its threads. Both 7th stud plates recovered exhibited rub marks consistent with fretting on both faces.

The number 2 cylinder hold down base flange clamp was not present on the 7th stud, and the stud threads contained dirt and grease.

The nut on the number 5 cylinder lower through bolt was not present.

ADDITIONAL INFORMATION

The wreckage was released on July 7, 2005.

NTSB Probable Cause

the separation of the number 4 engine cylinder due to improperly torqued cylinder hold down nuts. A finding in this accident was the lack of a shoulder restraint system in the airplane, which contributed to the occupants' injuries.