Failure - Interactions

Hidden damaged-wires

Cowan . . .  I was startled  ...  

    all  of a sudden,    there it was.

"Roll Correction and

                        Yaw Damper."  

Boeing Airliner 

(July-August, 1962),  pages 5-8.

Note:  this article from the manufacturer appeared during the investigation, AFTER the accident of  AA-Flt-One / 1Mar62.   Phrases  in the first paragraph (Airliner p5) are   the exact wording  later used  in the CAB's AAR

[AAR  released  15Jan63],  describing   yaw-roll coupling.  

The detailed insight from the manufacturer, alluded to Yaw Damper faults,  provided C.A.B. with system-background on that artificial-stability system,

          retrofitted into N7506A.

    Accident  Investigator

          evaluating  "Flight Test conditions":

        We  couldn't  accept

                             the   findings

                       as  representative  of what actually happened.

For   the   investigator:  

This was   George Van Epps'    main  lesson for you --

  a post-accident   "simulation" or   "flight test"  can yield  assertions from a most-respected-party:    assertions  that   you   should   suspect.   

 -- Check for    selective  favorable    data-dredging,  

 --  acknowledge     "voodoo correlations"    proposed as   "test results".

AUDIO only:

      Radio commentator

                Jean Shepherd,  WOR,

New York, set to cover a ticker tape parade  for astronaut John Glenn. Just as his radio- helicopter was taking off, word arrived of a crash at   Idlewild   Airport.

[Part One -- of a two part YouTube presentation.]


_NY Times_'  Dick Witkin  reviewed  

    various   Yaw x Roll            

          accidents since 1959.

B707- modification: Yaw Damper installed as a retrofit in N7605A:  This first  "parallel" Yaw Damper was OFF for takeoff and landing.   The location of the A/P panel, with the Y/D-Switch, was down on the Isle-stand, Center Console, just beneath the pilots' inboard elbow.

[The later "series" Y/D mod' installed a different Y/D- Switch on the Overhead Panel.]

     Yaw Damper

"... American Airlines 707 checklist specifies engagement of the yaw damper, of which the rudder servo is a component, shortly after takeoff. The heading trace ... changes from a wavering line to a straight line at 1007:38, suggesting yaw damper engagement at this instant." . . . 
[1007:38 = about ten seconds after lift-off ... LG-handle UP ...
​  . . . . . . speed increased near 187KIAS,  climbing past 200'agl].
B-707, early Autopilot Control Panel, center console (isle-stand)

  Departing  via Runway 31L,

      noise-abatement  TURN.

   Within 3-weeks after the accident

    Armbrister, T.  "Air crashes: Growing peril in the skies".

                _The Saturday Evening Post_,  V236 (January 19, 1963), 13-21, 68.

   investigation  prolonged, 

      flight tests not similar to mishap conditions

"The board normally holds its accident-investigation details secret until its official report is made public. However, in advance of today's report, board sources gave details of the findings to _The_Saturday_Evening_Post_."

​ "... investigation was prolonged because flight tests set up by the F.A.A. to test the servo theory were not carried out under the same conditions as the American Airlines flight.... charged the F.A.A. delayed and interfered with the official probe. The C.A.B. has the primary accident-investigation responsibility."

   An Engineer's Lesson

              every  new    engineered safety feature 

                              introduces a new failure-mode.

   An Engineer's Lesson

              every  new    engineered safety feature

                              introduces a new failure-mode.

 AAR  Pg 35-36   Review of

           aerodynamics of sideslip,

"... swept-wing airplanes are subject to a more pronounced  roll - yaw coupling than straight-wing airplanes.  When a swept-wing airplane with dihedral yaws, not only is the advancing wing at a higher angle of attack but it also presents a greater span to the airstream... lift differential ...  produces a greater rolling moment ... roll due to yaw  input of the rudder is much more pronounced...".

  CAB  Meeting

        January 15, 1963

    During the  nose-up  

1.4 g  banked  condition

     Impossible to  sense sudden yaw

  But,  during the upset,

                 suppose  you had

                                    pulled 1.4-G's ?

    "recovery capability would be much less."

  Boeing's  "Flight Tests"

          Pilots were able to recover

      June 3, 1962

    Air France B707 crash at Orly.

      June  through   September  1962:  

             Distractions  and  Delays   during an investigation.

      Investigative Costs  of the

         erroneous   Bolt-Scenario

  June 12th  -  15th

​                         1962

Witkin's-- disputed bolt-loss theory

Lessons from the past

        Bill Cook,    _The Road to the 707_ ,    pg 220:

. . .  Rudder should have had a hydraulic power servo and a Yaw Damper, as on the B-47  (these were added later on the 707).    Lessons from the past are too easily forgotten.    The 1939 accident of the 307 Stratoliner, mentioned previously in Chapter 4,  and the XB-47 dutch roll,  unfortunately had been forgotten by many,   including myself.   The original manual rudder  required hazardous flight training to simulate engine failures, and the risks from this training should have been minimized by the use of a power hydraulic servo . . . 

Real Estate demands of an investigation

Removal  of Wreckage layout:

During the investigation of TWA800,  during the late summer and fall of 1996, Structures Group members  moved  those  Floor Panels several times between various  Grumman hangers  at Calverton.   Later the NTSB  contracted to MOVE  the  entire  "reconstructed"  B747  fuselage Sections-42 &44  from   eastern  Long Island N.Y.,   to  Virginia  (to the new NTSB Training Center).

  B707  Fin-Rudder    Redesign  &  retrofit

            Vertical Stabilizer:   Size modifications,  AND   VENTRAL FIN;    

             Rudder:     retrofit of   Hydraulic Boost,   and

                               an   XB-47 style   "Yaw Damper"  

    Manipulating   "results"   inferred

     from  post-accident  "flight  testing"

           could   deceive   YOU  --  the  investigator.

  ?  Unwarranted  Assumptions  ?

     Disconnect Button:

                  Both  pilots had jammed  a  thumb 

                            against  their  disconnect switch

    Flight  Test  of a  Malfunction

    A   "Flight  Test":

         Let's  be  honest, 

    it's  just   not  the  same  . . .

    Cowan visits Bendix Plant

   "Show me  how  you do that."

    Wreckage  Examination

                        Done   at   Tulsa   (not at  Seattle).

   Examination of  new

                     stock parts

  Tiny wires from the  rate generator

        to the Yaw Damper


    Australian  Investigator

         Jim Brough

  Public  Hearing

   March  20th - 24th,   1962

    "We can't work with suppositions.   We can

        only deal in facts that reduce the zone of


    Flight Data Recorder 

  Maintenance   Records

  "Rudder kicks when

     boost is turned ON:

       Nose goes to left."

   Operations  Gp  Chmn

         Dick  Baker

Sat_Evening_Post pg18, left-col, para5-6
Wreckage examination, teardaown, Rudder Actuator, Servo, wires punctured.
Servo Looked Suspicious

   Systems Group Chmn

      Wesley Cowan

   Before the accident,

      Late  Jan' until  Feb'8th    jet  at  Seattle   for 

      Fin  Modification

Pan Am B707, 3Feb59   roll-upset  dive, over the North Atlantic.  Dives 29,000 ft.  [Waldo Lynch incident.]


Pan Am B707-120 / 25Feb59    N709PA   upset-separation of  #4 engine during   training,     S-W  of Paris.


AA- B707  / 15Aug59  Crew training:  excess yaw cited in 707 Peconic crash   (fatal).

Boeing Trainer / 19Oct59  violent Dutch Roll,  separation of 3 engines,  FIRE,  ditched-crashed  near Oso.  (Fatal.)

AA 1502 (trainer) /  28Jan61   B707-123  N7502A,      crashed off Montauk Point,  eastern Long Island, NY.   Sob = 6,  all killed.   

Sabena / 15Feb61   B-707, during approach- Go-around,  climbing turn.   rolling- dive- impact;  AAD # 13, pgs 43-5  "The Brussels Tragedy." 


  Air France   /   27Jul61   B707-328,

  F-BHAS,    T/O  Rwy-23  Hamburg;

   lost  directional-control:   veered left,  Rudder Pedal jam,    RTO,   yaw, NLG-wheels broke-away

          Runway Excursion,  off-side.

  "In  an  accident   investigation

​      EVERYTHING  is  suspect . . ."

  Structures Group  Chmn            Coe  Anderson

      YAW  x  Roll  =Dive !

    Climbing  left  Turn 

     B-707     N7506A

       AA flight One

     Thursday,   March 1,  1962


  Mid-January 1963

      Probable Cause

   C.A.B. offered

      INVESTIGATION  details to

           Saturday Evening Post: 

"The Board normally holds its accident-investigation

details secret  until its  official report  is made public.

  However,  in advance of today's report,

 Board  sources   gave details

of   the  findings  to   _The Saturday Evening Post_."   

 [ _Seattle Times_, Tuesday, Jan'15, 1963, pg 2.]


AA Flight One / March 1,  1962

   ". . .   'normal science'    means   research   firmly  based upon  . . .  past scientific achievements  . . .  

                       'paradigms'  . . .  relates  closely  to   'normal science' . . .  

                                                                 models   from which spring   particular   coherent  traditions  of  scientific research. . . .  

      The  study  of  paradigms   . . .  is what mainly  prepares the student   for membership in

the  particular    scientific community    with which  he will later practice.    

Because  he   there   joins   men   who  learned   the bases of their field    from the same concrete models . . .

  based on shared paradigms   are   committed  to   the same   rules  and  standards   for   scientific practice. . . ."     

 . . . . . . . . . Kuhn, Thomas S.  _The Structure of Scientific Revolutions:  50th Anniversary Edition_.  Revised, University of Chicago Press, 2012. 
. . . . . . . . . Ch 2, "The Route to Normal Science," pg 10-11.