A300 VERTICAL TAIL
STRUCTURAL EVALUATION
DESIGN FLAW IN LOWER REAR SPAR
By
Xavier J. Maumus
A300 VERTICAL TAIL
STRUCTURAL EVALUATION
DESIGN FLAW IN LOWER REAR SPAR
PART 1—DESIGN FLAW DETAILS
PART 2--FAILSAFE CRITERIA
PART 3--ULTIMATE CRITERIA
PART 4—FAILURE SCENARIO
A300 VERTICAL TAIL
STRUCTURAL EVALUATION
PART 1—DESIGN FLAW DETAILS
CRITICAL DESIGN FEATURE
Rear Reaction System
Spar Design Susceptible to Lateral
Deflection
Spar and Yoke Reaction System Designed Primarily to React
Lateral Load. Relieves Lateral Shear and Bending in the Main
Lugs.
Geometry makes Yoke Design Very Efficient in Resisting
Lateral Deflection.
Poor in Resisting Vertical Deflection.
.
DISCOVERY OF FLAW
NTSB Docket No. 168606, Factual Report 02-077, pg 9 of 63,
Section 2.2.2
Suspected Description of a Bearing Failure in LHS Rear
Transverse Spar Lug Located at the Upper/Outboard Edge of
the Lug Bore. This Failure Produced Substantial Compression
in the LH Yoke which is Inconsistent with the FEM Boundary
Loads.
Working Model Demonstrates that the Lower Rear Spar moves
to the Right which is necessary to Produce Compression Load
in the LH Yoke.
MECHANICAL LEVER
Lever Bar
Py
Vertical Tail
Main Lug Reaction
Rotation of Lever
Bar Develops
0 Resistance Ps
Yoke
Reaction
DESIGN FLAW
Geometry of Lower Rear Spar Design Produces a Mechanical
Lever (ML) in the Spar Reaction System.
As Aft Portion of the VT Deflects, its Lower Spar Rotates and
Produces Lateral Deflection at Spar Attachment to the Yokes.
Spar Reaction System is Very Efficient in Developing Lateral
Resistance.
Yokes Resist and Develop Large Internal Loads in VT Reaction
System.
Loads are Reacted at the Main Lugs (Shear and Out-of Plane
Bending) and Additive to the VT Loads.
REAR REACTION SYSTEM
FAILSAFE CONFIGURATION
Py
Fulcrum
ROTATION OF NO 1 RIB
AND REAR SPAR
.480 in.
Deflection of Lug
S
P
Rotation of Spar Produces Large Deflections at Yokes
LOAD DEVELOPMENT IN
LEVER MECHANISM

Spar Rotates and Produces Lateral Deflections at
its Lug Attachment to the Yokes

Yokes Resist Lateral Deflection and Develop Large
Internal Loads in Reaction System

Large Shear and Bending Loads are Reacted at the
Rear Main Lugs
MECHANICAL LEVERAGE
FAILSAFE CONFIGURATION
Vertical Movement of
Failed RHS Main Lug
Fulcrum—Located near Rib No. 1 in Skin
Transition Area above LHS Lug
Additional Side
Load Reacted at
LHS Main Lug
Transverse Spar Rotates
0
Counterclockwise about Fulcrum
Resistance to Spar Deflection
Develop Large Loads in Yokes
.480 in
EVIDENCE OF DESIGN FLAW
For Failsafe Criteria with the RHS Rear Main Lug
Disconnected, the FEM shows the RHS Lug moves to the Right
and Up.
Deflections Consistent with the Mechanical Leverage Model,
Shows Rotation of Spar.
Most Significant is the Deflection to the Right which Verifies
the Spar’s tendency to move Laterally. This Lateral Movement
is what Produces the Interference Resistance Between the Spar
and Yoke.
Working Model Demonstrates the Flaw.
Loads and Deflection Analysis Results are Consistent when
Mechanical Leveraging is Consisted.
FREEBODY OF LUG
Additional Load on Lug Bore
3.70
S
MXX
P
Lateral Resistance in Yokes Produce
Additional Shear and Bending in Lug
SIGNIFICANCE OF ML
Mechanical Leveraging makes the Design Susceptible to small
Deflections in the Lower Spar Structure.
Large Internal Loads are Produced in all members of the VT
Reaction Systems, Main Lugs are especially Susceptible.
Airbus FEM does not Account for Mechanical Leverage in the
Loads Analysis. FEM Deflections are Correct.
Mechanical Leverage supports a Pre-mature Failure in the
RHS Rear Main Lug below Ultimate
Renders Failsafe Capability Ineffective
TEST TO PROVE DESIGN FLAW
Full Scale Test
Failsafe Criteria
RHS Rear Main Lug Released
Apply Load
25% Limit BI 17
TEST CASE VS. AIRBUS FEM
CONDITION Rear Transverse Yokes
LHS
RHS
AIRBUS
8185
3747
TEST CASE
-1276
13203
Note the large load in the
RHS Yoke for Test Case
Vertical Tail and Rudder mounted on Aircraft
TEST TO PROVE DESIGN FLAW
Full Scale Test
Ultimate Criteria
Apply Load
25% Limit BI 17
TEST CASE VS. AIRBUS FEM
CONDITION Rear Transverse Yokes
LHS
RHS
AIRBUS
2373
-2363
TEST CASE
-1457
1457
Note the difference in sign
between the two load cases
Vertical Tail and Rudder mounted on Aircraft
TEST TO PROVE DESIGN FLAW






Perform Full Scale Calibration Test of Vertical Tail
on A300 Aircraft
Disconnect Fairings, Control Rods and Systems to
Avoid Damage to A/C
Mount Cameras to Record Movement of Rear Spar
Strain Gauge and Calibrate Aft Yokes
Apply Side Load (12,000 lb about 25% Limit Load) to
VT about 157 Inches Above Attachment
Read Gauges and Measure Rotational Deflection of
Rear Spar
Disconnect RHS Rear Main Lug and Repeat Test
Questions
The Effectiveness of the Mechanical Lever is Dependent on the
Location of the Fulcrum, how was this Point Located?
In the Failsafe Analysis, the Fulcrum is located near the
Intersection of the LH Skin and N0. 1 Rib. The Fulcrum
location is a Function of the Stiffness of Two Primary
Structural Members. One is the VT Box that is very Stiff and
whose Lower Side is Bound by the No. 1 Rib. The other being
the LH Main Lug Area whose Stiffness is a Function of its
Moment of Inertia and Fixity at the Lug Attachment. These
Stiffness Parameters Produce a Natural Inflection Point 2.83
inches above the Main Lug Bore.
In the Ultimate Criteria Analysis, no Fulcrum Location is
Determined. A .0125 inch Lateral Displacement is Assumed
since no FEM Defection Data is Available for Ultimate.
PHYSICAL EVIDENCE
Supports Mechanical Leverage

Bearing Failure in LHS Aft Transverse Spar Lug
Located at the Upper/Outboard Edge of the Lug Bore.
NTSB Docket No. 168606, Factual Report 02-077, pg 9
of 63, Section 2.2.2.
The Bearing Failure indicates that the Lower Spar
moved to the right to Produce this Failure.
Deformation of Left Transverse Yoke Sleeve. NTSB
Docket No. 168606, page 5 of 63.
A300 VERTICAL TAIL
STRUCTURAL EVALUATION
PART 2--FAILSAFE CRITERIA
DESIGN FLAW IN TRANSVERSE
SPAR
FAILSAFE CRITERIA

Requires That Vertical Tail Structure
Sustain Limit Load With One Major
Structural Member Failed
AIRBUS FAILSAFE PHILOSOHY

When one of the Main Lugs Fail, the Loads of that
Lug are Redistributed, Primarily to an Adjacent
Main Lug

In the Case of a Failure in the RHS Rear Main
Lug, 90% of the Load goes Forward and only 10%
is Resisted by the Yokes

In Order for this Redistribution to Occur the
Design must Allow the Failed Lug to Deflect
AIRBUS FAILSAFE ANALYSIS
Assumes RHS Rear Main Lug Fails
Results Based on Non-Linear FEM
Analysis—Set for Strain Solution
 Design Certification Lateral Gust
Condition at Limit Load
 LHS Spar Lug Critical
 Max Deflection of the Right Rear Main
Lug in A/C Coordinates is:
x = .004 in., y = .037 in and z = .480 in.

AIRBUS FEM RESULTS
Non-Linear Analysis
FAILURE ANALYSIS—RHS REAR MAIN LUG
FAILSAFE—BI17 LIMIT LOAD (LB)
Rear Transverse Yokes
LHS
RHS
Fx
Fy
Fz
Fres
-3890
-1781
31963
-14633
-5936
-2718
32742
14990
AIRBUS DETAIL ANALYSIS
LHS SPAR LUG CRITICAL
3.54
3.5
1.224 Dia.
4 1.224
DIA.
1.574
1.54
7
PLUG = 32,742 lb. LHS
Load Capacity of Lug = 40,271 lb. Ulti.
Margin of Safety = + .23 Limit
Critical for Shear Tear Out
MECHANICAL LEVERAGE
FAILSAFE ANALYSIS
Assumes Right Rear Main Lug Fails
 Results Based on Deflection Analysis
(Virtual Work)
 Considers Mechanical Leverage in
Lower Spar
 Design Certification Lateral Gust
Condition at Limit Load
 Deflection of the Right Rear Main Lug
in A/C Coordinates is:
y = .037 z = .480 in.
REAR REACTION SYSTEM
FAILSAFE CONFIGURATION
Py
Fulcrum
ROTATION OF NO 1 RIB
AND REAR SPAR
.480 in.
Deflection of Lug
S
P
Rotation of Spar Produces Large Deflections at Yokes
LOADS ANALYSIS
Analysis Considers Mechanical Leverage
FAILURE ANALYSIS—RHS REAR MAIN LUG
FAILSAFE—BI17 LIMIT LOAD
Rear Transverse Yokes Transition Area
LHS
RHS
LHS
Fx
Fy
Fz
Fres
607
-4984
926
-5105
-6275
-51556
-9575
52811
79724
DETAIL STRESS ANALYSIS
RHS SPAR LUG CRITICAL
3.54
3.5
1.224 Dia.
1.224
4
DIA.
PLUG = 52,811 lb. RHS
1.54
1.574
7
Load Capacity of Lug = 40,271 lb. Ulti.
Margin of Safety = - .24 Limit
Critical for Shear Tear Out
TRANSITION AREA
INTER-LAMINA SHEAR CRITICAL
20.00
PINTER-LAMINA SHEAR = 79724 lb.
1.17
SECTION A-A
A
A
UP
FWD
LOOKING
INB’D
LHS REAR MAIN LUG
Inter-lamina Shear Capacity = 50,215 lb. Ulti.
Margin of Safety = - .37 Limit
CONCLUSIONS
Based on Analysis Considering
Mechanical Leverage



RHS Rear Spar Lug will Fail at 76% of Limit
Load
LHS Rear Main Lug will Fail at 63% of Limit
Load
Vertical Tail does not Meet Failsafe Criteria when
Considering Mechanical Leverage
Question
The Component Tests were Used to Support Failsafe
Certification. Why didn’t this Flaw Show Up During those
Tests?
To my Knowledge none of the Spar Component Tests Included
Yokes attached to the Spar, so the Additional Internal Loads
from Mechanical Leverage wasn’t Allowed to Develop.
Additionally, Component Testing never Examined a Failsafe
Condition in which a Main Lug was disconnected.
The Boundary Loads used in all Component Tests were
Controlled by the FEM Loads Analysis that did not Account for
Mechanical Leverage.
A300 VERTICAL TAIL
STRUCTURAL EVALUATION
PART 3--ULTIMATE CRITERIA
ANALYSIS IS INCOMPLETE
NEED DEFLECTION DATA OF REAR SPAR
ULTIMATE CRITERIA

Requires That Vertical Tail Structure
Sustain 1.5 Times Limit Load Without
Failure of any Major Structural Member
AIRBUS ANALYSIS--ULTIMATE

Results Based on Non-Linear FEM
Analysis—Set for Strain Solution

Design Certification Lateral Gust Condition
at Ultimate Load

RHS Rear Main Lug Critical
AIRBUS FEM RESULTS
Non-linear Analysis
BI17 LOAD CASE—ULT.
S=
3,100 LB
P = 160,319 LB
MXX = 41,109 IN-LB
S
Margin of Safety = +.18
MXX
Critical for Shear Tear Out
P
RHS Lug
View looking Aft
REAR REACTION SYSTEM
NORMAL CONFIGURATION
Py
Py
Fulcrum
S
S
0
Pc
Pt
Rotation of Spar Produces Deflections at Yokes
MECHANICAL LEVERAGE
Mechanical Leverage Influences the Distribution of
Internal Load in Rear Reaction System
Fulcrum—Located near Rib No. 1
Additional Side Load
Reacted at LHS Main Lug
Additional Side Load
Reacted at RHS Main Lug
0
Rear Spar Rotates Counterclockwise
Produces Deflection at Lugs
Resistance to Spar Lateral Deflection
at Lugs are Developed in Yokes
DETAIL ANALYSIS RESULTS
Considers Mechanical Leverage
BI17 LOAD CASE—ULT.
NO DEFLECTION DATA AVAILABLE,
ASSUMES LATERAL INTERFERENCE
IN YOKES = .0125 IN.
(.030 Vertical Deflection of Rear Spar)
S=
26,075 LB
S
P = 160,319 LB
MXX = 74,376 IN-LB
Margin of Safety = - .13
Critical for Shear Tear Out
MXX
P
RHS Lug
View Looking Aft
CONCLUSIONS
Based on Analysis Considering ML

Assume Lateral Deflection of .0125 in. in Rear Spar
--Need Deflection Data--

Rear Main Lugs will Fail at 87% of Ultimate Load

Must be Substantiated by FEM Analysis and Full
Scale Static Test on Aircraft

Vertical Tail may not Meet Ultimate Criteria
Questions
The Full Scale Static Test was Used to Support Ultimate
Certification. The Test Article Failed at 126 % of Ultimate.
Why didn’t this Flaw Show Up During this Test?
The Full Scale Static Test didn’t Include Yokes, so the
Additional Internal Bending Load in the Rear Main Lugs from
Mechanical Leverage wasn’t Allowed to Develop.
The Boundary Loads of the Static Test were a Duplication of
the FEM Loads Analysis that did not Account for Mechanical
Leverage.
.
RECOMMENDATION
FEM ANALYSIS
Current Airbus FEM Internal Loads
Analysis needs Modification to Account for
Mechanical Leverage of Rear Spar
 FEM should be run on Non-linear set for
Geometry Solution

RECOMMENDATION
NTSB

Perform Proof Test

Full Scale Tests to Failure should be
Preformed for both Failsafe and Ultimate
Criteria
A300 VERTICAL TAIL
STRUCTURAL EVALUATION
PART 4—FAILURE SCENARIO
QUESTIONS
FAILURE SCENARIO
The RHS Rear Main Lug Failed First at below Limit and
Initiated a Series of Failures in the Rear Attachment System.





RHS Rear Main Lug Weakened by Overload Event 7 Years
Earlier--Second Wake Encounter
LHS Rear Main Lug--Thump
Rear Transverse Spar Lugs, RHS then LHS --Two Thumps
Rib No. 1 between Middle and Rear Spar– Snap and Loud
Thump
Fwd and Middle Main Lugs and Yokes Instantaneously–
Loud Bang
Questions
What Caused the RHS Rear Main Lug to Fail?
There is no way of knowing the exact Strength of the failed RHS
Main Lug, but in Part 3 of this Presentation, Ultimate Analysis
shows that the Lug might not meet Design Strength
Requirements when Mechanical Leverage is Considered.
The Lug had been Weakened by an Overload Event that
Occurred Seven Years Earlier. During this Event the Lug came
very Close to Failure and Caused Delamination around the Lug
Bore.
Increase Stress from the Mechanical Leverage Phenomena
caused further Delamination and Weakening of the Damaged
Lug Continued Until Failure.
QUESTIONS
How does Mechanical Leverage support Pre-mature Failure of
the RHS Rear Main Lug?
Bending Loads in the Lug are reacted at the Lug Bore and
Produce Strain in the Critical Outer Fibers of the Lug.
Mechanical Leverage Increases these Bending Strains making
the Lug even more Susceptible to Delamination.
If the Lug has been Damaged from a Previous Overload Event,
it is even more Susceptible to further Delamination.
As the Lug Continues to Weaken from Delamination, the
Bending Strains in its Outer Fibers are Driven to Larger
Levers Promoting Delamination Growth.
Questions
Why do you believe the RHS Rear Lug Failed below Limit?
My Analysis supports a Failure Scenario in which the RHS
Rear Main Lug may have been severely damaged from the
Overload Event that the Aircraft Experienced Seven Years
earlier. The Mechanical Leverage Effect Develops larger than
expected Bending Loads in the Lug that caused further
Delamination Growth.
Over the Years, the Lug continuously Weakens until it Prematurely Fails (below Limit Load) when Exposed to the Loads
of the Second Jet Wake Encounter about 17 Seconds before
Separation.
Questions
What Proof Exist to Support a Failure of the RHS Rear Main
Lug below Limit?
No Direct Evidence Exist to show that the Lug Failed below
Limit.
Failure Scenario Assumes that the Lug Ruptured at Second
Wake Encounter. Wake Encounter Load seems Less than Limit.
Need Analysis supported by Testing.
(Yes, you can say that Failsafe did not work but remember that
Airbus will say that it was a load beyond Limit that caused the
VT to go at once. You need some evidence that there was no
overload or that the intact system is not capable of carrying
the load.)
Questions
What Evidence Exist to Support a Zipper Type Failure of the VT?
This Presentation provides Physical Evidence and Failsafe
Analysis that Supports a Series of Failures (below Limit) in the
Rear Attachment System that may have Lasted a number of
seconds.
The Physical Evidence suggests a Series of Component Failures
that is Consistent with a Zipper Type Failure and takes some Time
to Develop because the Loading is not Overwhelming.
The Mechanical Leverage Design Flaw and Delamination
Damage of the other AA Aircraft proves a problem exist with the
Design.
Cockpit Voice Recording suggest that something was happening to
the Aircraft 17 seconds before the VT Departure.
Questions
What does the Voice Recording Suggest to you?
Its an indication that the Vertical Tail may have been coming
apart at least 17 seconds before separation from the aircraft.
During the time between 0915:51.8 and 0915:58.5, there are
recorded the sounds of three thumps, one snap, one loud thump
and one loud bang. These sounds were probably the sounds of
the VT's aft reaction system failing and No. 1 Rib breaking
apart with the last 'loud bang' at 0915:58.5 being the sound of
the simultaneous failure of the fwd and middle structure.
Questions
Why do you believe the LHS Rear Main Lug Failed before the
Rear Spar Lugs?
Failsafe Analysis in this Presentation shows the LHS Main Lug
to be more Critical than the Spar Lugs.
The Physical Evidence:
Two Large Areas of Delamination in the Lower Aft
Transverse Spar above both Lug Bores, NTSB Public Docket
No. 168624, Factual Report 02-078 App. A, page 9 of 52,
Figure 06. These Failures Result from Bending Produced by
Out-Of-Plane Loading on the Rear Spar.
These Delaminations Indicate that the Lower Spar moved
Substantially before Failure. In Order for the Lower Spar to
Move that much Meant that the LHS Rear Main Lug had to
be Disconnected.
PHYSICAL EVIDENCE
Supports Failure Scenario

Witness Marks on Forward LHS Aft Transverse Spar
Upper/Outboard Area between the Lug Bore and Rib No.
1. Roll No. 15-08-M.jpg.
Marks Result from Contact with the Outboard Edge of
the LH Yoke. Indicates that the Lower Spar moved
Substantially Downward and to the Right.
The Photo also shows the Bearing Failure at the Edge of
the Lug Bore of the Previous Slide. Failure located at
the 1 o'clock position.
PHYSICAL EVIDENCE
Supports Failure Scenario

Two Large Areas of Delamination in the Lower Aft
Transverse Spar above both Lug Bores, NTSB Public
Docket No. 168624, Factual Report 02-078 App. A, page
9 of 52, Figure 06. These Failures Result from Bending
Produced by Out-Of-Plane Loading on the Rear Spar.
Because the RHS and LHS Rear Main Lugs were Failed,
the Aft Structure of the VT was free to Twist. As this
occurred, Resistance Developed in the Yokes . The
Canted Transverse Spar rotated in a Vertical Plane about
the A/C Longitudinal Axis.
This Twisting of the aft structure could only occur while
the Fwd Structure remained Attached.
PHYSICAL EVIDENCE
Supports Failure Scenario

Witness Mark on the RHS Rear Main
Lug. Impact Damage to the Fracture Surface of
the Fwd Outboard Leg of the Lug may have
come from the VT moving to the right after
failure of the two Rear Main Lugs. The damage
was caused by contact with a piece of No. 1 Rib.
Roll No. 13-03-M.jpg
Questions
What was the Configuration of the VT at the Instant of
Departure?
Analysis supports a Failure Scenario in which the VT was
Supported only by the Fwd and Middle Attachment Systems at
Departure.
Ultimate Analysis shows that the RHS Rear Lug may be Under
Strength and Failsafe Analysis shows that the remaining Rear
Attachment System, LHS Main Lug and Yokes and the No. 1
Rib is not Capable of Sustaining Limit Load.
PHYSICAL EVIDENCE
Supports Failure Scenario

In order for the No. 1 Rib between the Aft and
Middle Spars to become Overloaded means that
the Rib became a Primary Load Member. The
Rib acted as a Cantilevered Beam and Attempted
to Restrain Movement of the Aft VT, and in doing
so, Provides effective Evidence that the Forward
Structure of the VT remained Intact and
Attached for some time after the Failure of the
Aft Reaction System.
Questions
What Load was on the VT at Time of VT Departure?
Consistent with Failure Scenario, at the Time of Complete
Failure and Departure of the VT only the Fwd and Middle
Reaction Systems were Attached.
Failure Load was Equal to the Strength of the LHS or RHS
Middle Main Lug and probably Less than Airbus’s Predicted
Load (192 % of Limit).
PHYSICAL EVIDENCE
Supports Failure Scenario
Lack of Witness Marks
NTSB Public Docket No. 168624, Factual Report 02-078
App. A, page 9 of 52, Figure 05. Middle Transverse Spar
shows no Out-of-plane Delamination Damage or Bearing
Failure in the LHS Lug Bore.
The two Forward and Middle Main Lugs Failed
Instantaneous and resulted in no Out-of-plane
Delamination in the Middle Spar. As the VT departed,
the VT Structure was free to move aft and vertically in
the plane of the Canted Spar, and hence, no Out-of-plane
Resistance produced by the Yokes.
NTSB Public Docket No. 168606, page 5 of 63. Both
Forward and Middle Yokes were free to rotate on their
Lower Attach bolts.
Questions
How do you Explain Airbus’s Prediction of a Failing Load of
192% of Limit?
Airbus’s Load Prediction is Based on a Fully Effective Rudder
and Fin Completely Supported by the Fwd, Middle and Rear
Attachment Systems.
In Failure Scenario at the Time of Departure, the VT was only
Supported by the Fwd and Middle Attachment Systems and
Missing the Aft Section of No. 1 Rib. This Configuration
Reduced the Effectiveness of both the Rudder and Fin which in
turn, Restricted Load Development on the VT System.