Trip7
Well-Known Member
From a co-workers Father who worked for Douglas..................
What happened here (in Narita) is the same as what happened in Hong Kong
(to a China Airlines MD-11) and Newark NJ (to another FedEx MD-11) some
years ago. The hard landings, which resulted in ALL cases from failure of the
aircraft to respond appropriately to pilot control inputs, resulted in
rupture of the wing spar by the main gear oleo strut, breaking the wing; the
lift from the wing not yet broken then caused the aircraft to roll, and turn
upside down. In the case this morning, both wings broke - first the left,
and then as the roll angle reached about 80° LWD, the right wing also broke.
this can be seen clearly on the video presented on the BBC News website.
The failure of the aircraft to respond appropriately to pilot control
inputs is the result of certification of the aircraft despite the omission of a
vital part of the aircraft flight control system: namely the rate command
function of the LSAS system. This omission leads, under certain
circumstances, to what can be described as a "cliff-like" APC* as a result of the
extremely slow response of the airplane to elevator control inputs at high
gross landing weights. Despite protestations by the Douglas Aircraft Co. that
the aircraft flies "just like a DC-10" (which are blatant untruths) the
airplane is inherently dangerous and extremely difficult to handle in gusty
wind conditions, especially at high landing weights.
I have had many discussions with FedEx ( and Delta) pilots and instructors
about the MD-11, and have invariably heard horror stories about landings.
I feel a great sense of sadness for the families of the airmen who were
victims of this tragedy, and I know that sadness will turn into anger when
once again the NTSB/Boeing clique start to insist that this was all caused by
pilot error.
I am once again reminded of a statement by the chief investigator of the
Hong Kong MD-11 accident, Mr. Robert Benzon, who, in the presence of several
Boeing engineers, the Asst. VP of flight safety at China Airlines, and
myself, said: "...sometimes we have to burn a couple of pilots to protect the
local industry..." Not this time, Mr. B.
* "cliff-like" APC
Airplane-Pilot-Coupling - the phenomenon used to be called PIO, but the
name was changed so to avoid the implication of pilot causality.
A more complete description of this aircraft design/response problem can
be found in Aviation Safety and Pilot Control published by the National
Research Council. ISBN-10: 0309056888
The terms stability, stable, and unstable have specific meanings with respect to the flying qualities of an airplane. Those meanings are confined to "static stability" and "maneuvering stability" and refer to control force gradients vs. speed, and vs. normal acceleration ('g') respectively. Unfortunately, in common practice the terms are used indiscriminately by "aviation experts".
The software changes (implementation of the -908 FCS load, and some subsequent set mandated by the FAA to allow certification of the MD-10 on the same type cert) improved the predictability of the MD-11 in the landing phase; they did nothing to correct the omission of a simple lead-lag pitch SCAS (à la F-4) which was designed into the Rate Command CWS of the LSAS (which is there, but set to zero gain, making it non-functional), which would have compensated for the extremely low short period natural frequency of the airplane in the landing configuration (making the airplane prone to APC). The change in geometry from DC-10 to MD-11 made this item a required addition from a handling qualities standpoint, yet the FAA still certified the airplane. They also did nothing to correct the gross elevator load feel (force vs. displacement) gradients in the landing configuration, which make it virtually impossible for a normal pilot (and in particular a soft-handed airline pilot) to access the necessary deflections for control of the airplane. Nor did they compensate for the inadequate bandwidth of the elevator hydraulic actuators, which incur significant lags when rapid elevator control inputs are required (as in turbulence).
The DC-10, and MD-10, does not suffer from the above problems for several reasons: it has a lower max landing weight, and thus much reduced pitch inertia (Iyy), the elevator throws required for adequate control are significantly reduced as a result of greater elevator control power (area) along with correspondingly lower required control forces. Additionally, the DC-10 (as employed at most airlines) does not employ RCWS, a ludicrous, parallel roll control "enhancement" on most MD-11s; FedEx, incidentally, ordered its airplanes to have RCWS turned off; a wise decision.
What happened here (in Narita) is the same as what happened in Hong Kong
(to a China Airlines MD-11) and Newark NJ (to another FedEx MD-11) some
years ago. The hard landings, which resulted in ALL cases from failure of the
aircraft to respond appropriately to pilot control inputs, resulted in
rupture of the wing spar by the main gear oleo strut, breaking the wing; the
lift from the wing not yet broken then caused the aircraft to roll, and turn
upside down. In the case this morning, both wings broke - first the left,
and then as the roll angle reached about 80° LWD, the right wing also broke.
this can be seen clearly on the video presented on the BBC News website.
The failure of the aircraft to respond appropriately to pilot control
inputs is the result of certification of the aircraft despite the omission of a
vital part of the aircraft flight control system: namely the rate command
function of the LSAS system. This omission leads, under certain
circumstances, to what can be described as a "cliff-like" APC* as a result of the
extremely slow response of the airplane to elevator control inputs at high
gross landing weights. Despite protestations by the Douglas Aircraft Co. that
the aircraft flies "just like a DC-10" (which are blatant untruths) the
airplane is inherently dangerous and extremely difficult to handle in gusty
wind conditions, especially at high landing weights.
I have had many discussions with FedEx ( and Delta) pilots and instructors
about the MD-11, and have invariably heard horror stories about landings.
I feel a great sense of sadness for the families of the airmen who were
victims of this tragedy, and I know that sadness will turn into anger when
once again the NTSB/Boeing clique start to insist that this was all caused by
pilot error.
I am once again reminded of a statement by the chief investigator of the
Hong Kong MD-11 accident, Mr. Robert Benzon, who, in the presence of several
Boeing engineers, the Asst. VP of flight safety at China Airlines, and
myself, said: "...sometimes we have to burn a couple of pilots to protect the
local industry..." Not this time, Mr. B.
* "cliff-like" APC
Airplane-Pilot-Coupling - the phenomenon used to be called PIO, but the
name was changed so to avoid the implication of pilot causality.
A more complete description of this aircraft design/response problem can
be found in Aviation Safety and Pilot Control published by the National
Research Council. ISBN-10: 0309056888
The terms stability, stable, and unstable have specific meanings with respect to the flying qualities of an airplane. Those meanings are confined to "static stability" and "maneuvering stability" and refer to control force gradients vs. speed, and vs. normal acceleration ('g') respectively. Unfortunately, in common practice the terms are used indiscriminately by "aviation experts".
The software changes (implementation of the -908 FCS load, and some subsequent set mandated by the FAA to allow certification of the MD-10 on the same type cert) improved the predictability of the MD-11 in the landing phase; they did nothing to correct the omission of a simple lead-lag pitch SCAS (à la F-4) which was designed into the Rate Command CWS of the LSAS (which is there, but set to zero gain, making it non-functional), which would have compensated for the extremely low short period natural frequency of the airplane in the landing configuration (making the airplane prone to APC). The change in geometry from DC-10 to MD-11 made this item a required addition from a handling qualities standpoint, yet the FAA still certified the airplane. They also did nothing to correct the gross elevator load feel (force vs. displacement) gradients in the landing configuration, which make it virtually impossible for a normal pilot (and in particular a soft-handed airline pilot) to access the necessary deflections for control of the airplane. Nor did they compensate for the inadequate bandwidth of the elevator hydraulic actuators, which incur significant lags when rapid elevator control inputs are required (as in turbulence).
The DC-10, and MD-10, does not suffer from the above problems for several reasons: it has a lower max landing weight, and thus much reduced pitch inertia (Iyy), the elevator throws required for adequate control are significantly reduced as a result of greater elevator control power (area) along with correspondingly lower required control forces. Additionally, the DC-10 (as employed at most airlines) does not employ RCWS, a ludicrous, parallel roll control "enhancement" on most MD-11s; FedEx, incidentally, ordered its airplanes to have RCWS turned off; a wise decision.
