Failure - Interactions
Cowan . . . I was startled ...
all of a sudden, there it was.
"Roll Correction and
(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.
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".
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.]
"... 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].
. . . 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 . . .
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).
lost directional-control: veered left, Rudder Pedal jam, RTO, yaw, NLG-wheels broke-away
"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_."
'paradigms' . . . relates closely to 'normal science' . . .
. . . . . . . . . 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.
"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."
"... 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...".