Incidents & Accidents
Incident occurred Monday, April 28, 1997 at SPOKANE, WA
Aircraft:Beech 35, registration: N2839V
Injuries: 1 Uninjured.
The pilot reported that he was conducting a maintenance test flight. He was
flying straight and level at 160 mph. The sky was 6,500 feet broken with
smooth air. The pilot reported that the airplane started to vibrate. He
reported that the vibration started as a minor shake and intensified 'like
an earthquake.' The pilot pulled the throttle immediately (less than 3
seconds) and the vibration stopped. An uneventful landing was made. The
inspection to the airplane revealed no visible damage. The pilot reported
that the vibration was the same kind of vibration that he experienced in the
same airplane on August 1, 1996. The only changes made to the airplane since
the first vibration had been the installation of a B35 model bulkhead, and
the installation of F35 model equivalent counterweights. The airplane
exhibited no anomalies. The ruddervators were properly balanced.
The National Transportation Safety Board determines the probable cause(s) of
this accident as follows.
the vibration of the fuselage was due to flutter.
Accident occurred Monday, October 06, 1997 at POPLAR GROVE, IL
Aircraft:Beech G35, registration: N129B
Injuries: 2 Uninjured.
The pilot reported that he was cruising at 4,000 feet msl in clear sky
conditions with smooth air, then he initiated a descent. He said that while
descending through about 3,200 feet msl at 185 mph with a 5 degree nose down
attitude and 15 degree left turn, the control yoke started oscillating fore
and aft about 1/2 inch. The oscillations increased to about 1 inch fore and
aft, and the airplane experienced 3 or 4 'solid jolts.' After about 5
seconds, the pilot reduced power, and the vibrations stopped. He continued
to his destination and landed uneventfully. According to the Pilot
Operating, the airplane's never exceed airspeed (Vne) was 202 mph. The
maximum cruise airspeed (Vno), was 175 mph. Inspection of the airplane
revealed that the aft fuselage received extensive damage between fuselage
station (FS) 256.9 and the 233.5 bulkhead. The longerons were bent downward
with a permanent 2.5 to 3 inch bend. The left and right side fuselage panels
below the stabilizers exhibited 45 degree buckling from the bottom of the FS
256.9 bulkhead to forward of the stabilizer cuffs. The bottom fuselage panel
forward of the 256.9 bulkhead had popped rivets and torn skin. There were
three creases in the right stabilizer. No pre-existing cracks were found on
the longerons. The ruddervators were properly balanced.
The National Transportation Safety Board determines the probable cause(s) of
this accident as follows.
flutter for an undetermined reason, which resulted in structural damage to
the aft fuselage.
Accident occurred Tuesday, April 29, 1997 at LEXINGTON, KY
Aircraft:Beech D35, registration: N5985C
Injuries: 2 Uninjured.
The pilot reported that he made a climb to 7,500 feet and set his power to
cruise at 160 mph. To remain clear of clouds, he started a descent to 6,500
feet. He experienced light turbulence, and the airplane began to vibrate and
shake. After 10 to 15 seconds, the pilot pulled back on the throttle, and
the vibration stopped. The pilot thought the vibration was engine related.
He re-applied power for cruise, then the airplane started to shake again,
but much more violently than the first occurrence. He reduced power and
landed the airplane. The airplane's never exceed airspeed (Vne) was 203 mph,
and the maximum cruise airspeed (Vno) was 160 mph. Inspection of the
airplane revealed that the aft fuselage received extensive damage between
fuselage station (FS) 256.9 and the 233.5 bulkhead. The longerons were bent
downward, and two stringers were cracked. The left and right side fuselage
panels below the stabilizers exhibited 45 degree buckling from the bottom of
the FS 256.9 bulkhead to forward of the stabilizer cuffs. The bottom
fuselage panel had popped rivets and torn skin, and there were two 2-inch
creases in both stabilizers. No pre-existing cracks were found on the
longerons. The ruddervators were properly balanced.
The National Transportation Safety Board determines the probable cause(s) of
this accident as follows.
flutter for an undetermined reason, which resulted in structural damage to
the aft fuselage.
Accident occurred Monday, April 13, 1998 at BENTONVILLE, AR
Aircraft:Beech B35, registration: N5246C
Injuries: 2 Uninjured.
The pilot reported that the airplane was just leveling off after a descent
of 700 feet. The wind was light in smooth air. The airplane was in a 15
degree angle of bank right turn, 1 to 2 degrees nose down attitude, and at
180 mph. The airspeed was in the middle of the yellow arc. The pilot
reported the airplane began to shake violently like a rivet gun hitting
against the fuselage, or like a machine gun. He said the vibrations
reverberated throughout his body. He did not feel any vibrations in the
controls. He pushed over on the control column after about three seconds of
vibration. The vibration stopped. An uneventful landing was made. The
aircraft inspection revealed cracks in the upper two corners of the FS 256.9
bulkhead. The forward spar of the right ruddervator was broken. A crack had
proceeded through the top spar flange and had worked its way down to the
bottom flange but stopped about 1/4 inch prior to reaching a rivet hole. The
center hinge had broken and a 8.5 inch skin tear was evident on the top
surface of the ruddervator. The ruddervators were properly balanced. The
inspection revealed no maintenance anomalies. The FAA issued an
Airworthiness Directive 98-13-02 on July 7, 1998, restricting the airspeed
to 144 mph on Beech 35, A35,and B35 airplanes. The aircraft manufacturer
issued a Service Bulletin 27-3358 in February 2000, which required an
extensive inspection of empennage components, and it changed the ruddervator
underbalance from 16.8 to 19.8 inch pounds to 16.8 to 18.0 inch pounds in
order to lift the speed restriction.
The National Transportation Safety Board determines the probable cause(s) of
this accident as follows.
the damage to the empennage was due to flutter.