Premium on Safety - Issue 44, 2022 - 11

LESSONS LEARNED
it began a descending right turn off course, losing 700 feet in
the first five seconds and 6,900 in the next 14-a descent rate
approaching 30,000 feet per minute. The last radar hit, recorded
at 12:40:09 just southeast of the eventual location of the wreckage,
was made at 6,200 feet. One witness about a mile away heard a
" high-speed, high-pitch engine sound " followed by " three booms,
and then silence. " A second, a pilot of 44 years experience, heard
the airplane fly over and described the engines as " screaming. "
Investigators found the lightest pieces, including pieces of insulation
and interior components, the rudder counterweight, and fragments
of the elevators at the extreme southern end of the debris field.
Both engines were at the far northern end, 278 feet apart. The
right wing, cockpit, and empennage lay between the inboard and
outboard sections of the left wing, with the aft section of the cabin
456 feet east of the cockpit. The center section of the fuselage and
the center wing section that ran through it were shattered when
all three wing spars failed in overload; after reconstruction, they
showed various deformations in both the up-and-down and foreand-aft
directions. Matching transfer marks and propeller gouges
showed that the right engine struck the left wing after separating
from its mounts. Though there was a 90% probability of icing at the
Conquest's cruising altitude, there was no evidence of airframe ice
accumulation.
The NTSB concluded that, " The structural failure signatures on the
airplane were indicative of the wings failing in positive overload,
which was consistent with the pilot initiating a pull-up maneuver
that exceeded the airplane spars' structural integrity during an
attempted recovery from the spiral dive. " Officially, probable cause
was found to be, " The pilot's failure to maintain control of the
airplane in dark night conditions that resulted in an in-flight positive
overload failure of the wings and the subsequent in-flight break-up
of the airplane. "
But why did a 4,700-hour airline transport pilot and instrument
instructor whose experience included 3,500 hours of multiengine
time, 590 hours at night, and 400 in actual IMC fail to notice his
airplane entering an unusual attitude before its vertical velocity
became catastrophic? The investigation revealed no clues. The
manufacturer was able to extract and read the memory card from
the airplane's KMH-820 Multi-Hazard Awareness Unit, but found
that it recorded no useful data on the accident flight. A message
recovered from the pilot's mobile phone indicated that on a flight
six days earlier, the horizontal situation indicator had precessed 25
degrees, but the autopilot had continued to hold altitude and track
nav inputs. The radar track of the accident flight showed that it
remained on course and level until the moment of departure.
Owners and operators are understandably less than enthusiastic
about installing expensive equipment not required by regulation,
particularly when it's only useful in reconstructing accidents, not
preventing them. In their absence, some tragedies will simply
remain unexplained.
-David Jack Kenny is a freelance aviation writer and
statistician.
11
Premium on Safety - Issue 44, 2022

Table of Contents for the Digital Edition of Premium on Safety - Issue 44, 2022
