But what was the real cause of
all the loss of control training accidents?
Investigators of the 1960's, '70's, early '80's,
would have you believe that it was
simply a case of pilot error.
As we now know it [training mishap fatalities]
were a result of poorly designed and
improperly certificated airplanes ...
attempting to fly with thrust-asymmetry
[engine failure] at too low speeds.
This hindsight conclusion is
not meant to cast any aspersions on anyone . . .
but only to put into perspective
the evolution of the design of jet transports. . . .
To understand this, it is necessary to review
just how the aircraft were certificated
for minimum control speed.
Marthinsen, H.F. "Engine-Out Flight Training Revisited". Presented at ISASI's 13th Int'l Seminar, Tel Aviv, Oct' 11-15, 1982; ISASI Proceedings 1982, p46-63.
. . . the beginning of rudder "blowback,"
where the rudder hinge moment is overcome by slipstream forces
and causes the rudder to streamline . . .
The Board determines the probable cause of this accident was the crew's failure
to recognize and correct the development of excessive yaw
which caused an unintentional rolling maneuver
at an altitude too low to permit complete recovery.
[C.A.B.'s AAR, p11.]
By the first week of February 1960,
UK's ARB had withheld certification of B-707;
more than a year before the C.A.B.'s accident report was adopted,
the manufacturer initiated Fin-Rudder modifications:
and the hydraulic-boost,
with an anti-balance Tab.
The initial B707 Rudder-design was for
a manual Tab, a "balance" Tab: no hydraulic-boost.
The Rudder Pedals were connected to the Tab, the Tab then flew the Rudder.
Initial Fin-Rudder design:
a shorter-height VertStab, Rudder -- manual, spring- Tab [no hydraulic boost].
The early B-707 Rudder was operated only by aerodynamic forces on the TAB and
by differential pressures acting on
the BALANCE PANELS ahead of the rudder Hinge Line on the fin.
Per _Flight_, 25July58, p145:
"Flying Controls Internal balance plates, aerodynamic tabs . . . are the basis of
the Boeing 707's mainly manual control system, which also provides proportional feel,
but rudder boost is used on the 707-220 and Intercontinental models
for maximum rudder deflection in the low-speed, engine-out case...."
A public hearing was ordered by the Board and held in two phases.
The operational phase of the investigation was held
at the Henry Perkins Hotel, Riverhead, Long Island, New York,
on August 27, 1959.
The technical phase of the investigation was held at
the Forest Hills Inn, Forest Hills, Long Island, New York,
October 7, 1959.
Press story reported on first day of Public Hearing, Thursday, August 27th 1959:
Thrust asymmetry, yaw, roll.
Failure - Interactions
B-707 Service Bulletin dated Feb' 5th, 1960 .
" . . . the machine was already FAA-certificated . . .
the FAA Test Pilot had not been supported by Washington,
in his attempt to reject the airplane."
"... It came as something of a shock . . . that following flight tests by ... Air Registration Board ...
British approval of the 707 was still withheld...
it was lateral behaviour . . . at slow speeds ... called to question ...
ARB’s Chief Test Pilot,
D.P. Davies Interview —
Davies recalls his battle with Boeing,
FAA, the ARB’s Board,
over the certification of the Boeing 707 .
D.P. Davies’ commentary about
early B-707 S&C testing
begins at audio-time of 1h:14m:32s .
"... The Boeing 707 really was one of the world's
leaders in big transport airplanes . . .
the first . . . bought by BOAC was
one of the big intercontinental -436' s.
. . . a big hairy-chested aeroplane.
But it was unreasonably demanding to fly.
The primary flight controls were ... manual
– in spite of its size – ...
... But the other thing was that
it was very heavy to fly. . . .
. . . there were large problems
in directional stability & control .
Fundamentally the Fin was too small.
And this led to all the problems associated –
divergent Dutch Roll,
violent roll following engine failure inflight,
high minimum control speeds [inflight],
all compounded by high foot-forces
in engine-out conditions, and
extremely high foot forces
in [1:16:14] two-engine-out conditions.
. . . all made worse by . . .
the unachievable LOW
[published] minimum control speeds
on takeoff, and on go-around,
... I was appalled . . .
It didn't take any wit . . .
to turn the aircraft down . . .
Boeng simply couldn't believe that we
were turning the airplane down.
More details from the C.A.B.'s "Peconic" investigation on next page
. . . [these notes are still in-progress so scroll through that next page ... ]
The various Fin-Rudder modifications continued through the next decade, with the Rudder-TAB rotation redesigned to an Anti-Balance function, with various "boost" iterations [from the initial manual-Tab to a "power augmented rudder" then later a "full range boosted Rudder"] , and various iterations of Rudder-Tab ratios. The artificial stability was added: first effort was the "parallel" Yaw Damper, then after AA Flt-One, a redesigned "series" Yaw Damper.