THE OFFICIAL PUBLICATION FOR BONANZA, BARON & TRAVEl ...

ABS-ASF spar web investigation
It is difficult to project the facts in a dynamic situation when there is a sig·
nificant delay between the time of reporting and publishing. I'm writing
this in early March while you are reading it in mid·April. by which time I
hope some importa nt and positive events will have taken place. Please
bear with me as I bring you up to date on where we are right now.
How we got to where we are
As you know, a substantial part of the fleet is operating
under two Airworthiness Directives (ADs)--{)ne for Bonanzas
and Debonairs and another for Travel Airs and Barons-that
require periodic inspections of the front wing spar carry-thru
assembly for cracking, monitoring any cracks found and
repairing them if they grow beyond specified limits.
In 1996 the FAA adopted a policy that no longer allows
continued operations wi th any cracks in primary structure, and
in 2004 they notified ABS of their intention to revise the ADs
to impose that "no cracks" policy on our airplanes. The only
approved repair is installation of a doubler kit supplied by the
Beech factory. This repair is very difficult to accomplish correctly
and everyone agrees that improper installation poses a
real threat to the integrity of the airframe.
We have been operating under the inspection and monitoring
program for 20 years and have a fleet-wide history of
perhaps 60 mi//ioll flight hOllrs without a single mishap.
Furthermore, in 2004 there was a growing body of qualified
engineering opinion that the repair kit did not address the root
cause of the cracki ng. In view of the fleet history, engineering
opinions and the difficulties and risks associated with the
repair, the ABS Technical Committee was concemed that
eliminating the crack-monitoring program and requiring
installation of the doubler kit in all cracked airplanes might not
be in the best interests of our members.
Although we asked, the factory was unwilling to share
any engineering information. Consequently, the ABS Air
Safety Foundation engaged two highly regarded consulting
engineers to review the situation. Although suggesting a probable
cause of the cracking, more importantl y, the reports recommended
further study.
ABS-ASF then sought bids and eventually contracted for
an engineeri ng study to definitively determine the cause of the
cracking and analyze the safety issues involved. Although we
clearly hoped the study would provide the engineering basis
for continuing the inspection and monitoring program. our primary
goal was to understand the physics of the structure, the
loads imposed on it, what was causing the craCking and to
what extem small cracks posed a safety issue.
Responding to our request, the FAA has held off on further
action to allow us time to complete our investigation and
has indicated they wi ll review and consider the results of that
investigation in their final evaluation. Their forbearance in giv-
ing us this window has been greatly
appreciated.
The study contract
The investigation was conducted
by J.B. Dwerlkotte Associates (JBDA)
and consisted of developing a computer
model (finite element model) of the
airframe and the carry-thru structure, developing the loads to
apply, instrumenting an aircraft (thanks to owner Robert
Majoros), gathering stress data from actual flights, predicting
crack propagation and analyzing and drawing conclusions.
We received the contract fina l report from JBDA in
ovember 2007. It is not an exaggeration to describe it as a
very hefty document, both in terms of its physical size as well
as its depth of content. It has been a real challenge for our
Tech nical Committee to absorb its substance and put it in
proper perspective. There was no way we could do that on our
own and we relied heavily on our engineeri ng consultant,
retired Boeing chief of structures engineering Peter Harradine.
We have gone through about six rounds of detailed questions
and answers, including several hours on the phone with JBDA.
The bottom line is that the study is inconclusive in sever·
al key areas. It just doesn't go far enough to get the answers
that we need. That is not to say the study didn 't yield impor.
tam insights and it does provides ABS-ASF with some really
valuable anal ysis and data. But we are not able to answer some
critical questions, at least not to the level of engineering certainty
that we feel is necessary to go forward.
JBDA worked diligently, accomplished a great deal and
has been extremely cooperati ve during this review period and
we have concluded their contract.
Where we want to go
JBDA and Peter Harradine are in total agreement that a
fo llow-on phase of the investigation, expanding on the work
already performed, should yield the definitive answers that we
eek. There is no question that we have come a long way down
the road of understanding, but we know we are not yet at our
destination. Consequently, the Technical Committee has asked
Peter to prepare a statement of work for a subsequent contract
to take the investigation to the next level, and JBDA has agreed
to perform the work in the near term.
When we have an agreed-upon statement of work, price
and schedule, we will determine whether to expand the investigation.
If we decide to proceed, we'll then ask the FAA for
their continued patience to allow us to complete it.
By the time you read thi , we may have already
announced the outcome on our website. If so, you already
know how it comes out I hope you're smiling!
Until next momh. -Art
ABS April 2008 www.bonanza.org Page 10710