Newsgroups: sci.aeronautics.airliners
From: rdd@rascal.ics.utexas.edu (Robert Dorsett)
Subject: NTSB DC-10 excerpts
Date: Wed, 25 Nov 92 02:26:16 CST

It's been about two years since I last posted this, so...


--------------------

Excerpts from the NTSB accident report on the Chicago O'Hare crash:

Synopsis:

About 1504 CDT, May 25, 1979, American Airlines Flight 191, a McDonnell-Douglas
DC-10-10 aircraft, crashed into an open field just short of a trailer park about
4600' northwest of the departure end of runway 32R at Chicago-O'Hare Internat-
ional Airport, Illinois.

Flight 191 was taking off from Runway 32R.  The weather was clear and the vis-
ibility was 15 miles.  During the takeoff rotation, the left engine and pylon
assembly and about 3 ft of the leading edge of the left wing separated from
the aircraft and fell to the runway.  Flight 191 continued to climb to about
325' above the ground and then began to roll to the left.  The aircraft con-
tinued to roll to the left until the wings were past the vertical position,
and during the roll, the aircraft's nose pitched down below the horizon.

Flight 191 crashed into the open field and the wreckage scattered into an
adjacent trailer park.  The aircraft was destroyed in the crash and subsequent
fire.  Two hundred and seventy-one persons on board Flight 191 were killed;
two persons on the ground were killed, and two others were injured.  An old
aircraft hangar, several automobiles, and a mobile home were destroyed.

The National Transportation Safety Board determines that the probable cause
of this accident was the asymmetrical stall and the ensuing roll of the air-
craft because of the uncommanded retraction of the left wing outboard leading
edge slats and the loss of stall warning and slat disagreement indication sys-
tems resulting from maintenance-induced damage leading to the separation of the
No. 1 engine and pylon assembly at a critical point during takeoff.  The sep-
aration resulted from damage by improper maintenance procedures which led to
failure of the pylon structure.

Contributing to the cause of the accident were the vulnerability of the design
of the pylon attach points to maintenance damage; the vulnerability of the
design of the leading edge slat system to the damage which produced asymmetry;
deficiencies in Federal Aviation Administration surveillance and reporting sys-
tems which failed to detect and prevent the use of improper maintenance proced-
ures; deficiencies in the practices and communications among the operators,
the manufacturer, and the FAA which failed to determine and disseminate the
particulars during previous maintenance damage incidents; and the intolerance
of prescribed operational procedures to this unique emergency.



Findings (p. 67)

1.  The engine and pylon assembly separated either at or immediately after
takeoff.  The flightcrew was committed to continue the takeoff.

2.  The aft end of the pylon assembly began to separate in the forward flange
of the aft bulkhead.

3.  The structural separation of the pylon was caused by a complete failure of
the forward flange of the aft bulkhead after its residual strength had been
critically reduced by the fracture and subsequent service life.

4.  The overload fracture and fatigue cracking on the pylon aft bulkhead's
upper flange were the only preexisting damage on the bulkhead.  The length of
the overload fracture and fatigue cracking was about 13 inches.  The fracture
was caused by an upward movement of the aft end of the pylon which brought the
upper flange and its fasteners into contact with the wing clevis.

5.  The pylon to wing attach hardware was properly installed at all attachment
points.

6.  All electrical power to the No. 1 AC generator bus and No. 1 DC bus was
lost after the pylon separated.  The captain's flight director instrument, the
stall warning system, and the slat disagreement warning light systems were
rendered inoperative.  Power to these buses was never restored.

7.  The No. 1 hydraulic system was lost when the pylon separated.  Hydraulic
systems No. 2 and No. 3 operated at their full capability throughout the flight.
Except for spoiler panels No. 2 and No. 4 on each wing, all flight controls
were operating.

8.  The hydraulic lines and followup cables of the drive actuator for the left
wing's outboard leading edge slat were severed by the separation of the pylon
and the left wing's outboard slats retracted during climbout.  The retraction
of the slats caused an asymmetric stall and subsequent loss of control of the
aircraft.

9.  The flightcrew could not see the wings and engines from the cockpit.
Because of the loss of the slat disagreement light and the stall warning system,
the flightcrew would not have received an electronic warning of either the slat
asymmetry or the stall.  The loss of the warning systems created a situation
which afforded the flightcrew an inadequate opportunity to recognize and
prevent the ensuing stall of the aircraft.

10.  The flightcrew flew the aircraft in accordance with the prescribed emer-
gency procedure, which called for the climbout to be flown at V2 speed.  V2
was 6 KIAS below the stall speed for the left wing.  The deceleration to V2
speed caused the aircraft to stall.  The start of the left roll was the only
warning the pilot had of the onset of the stall.

11.  The pylon was damaged during maintenance performed on the accident aircraft
at American Airline's Maintenance Facility at Tulsa, Oklahoma, on March 29 and
30, 1979.

12.  The design of the aft bulkhead made the flange vulnerable to damage when
the pylon was being separated or attached.

13.  American Airlines engineering personnel developed an ECO to remove and
reinstall the pylon and engine as a single unit.  The ECO directed that the
combined engine and pylon assembly be supported, lowered, and raised by a
forklift.  American Airlines engineering personnel did not perform an adequate
evaluation of either the capability of the forklift to provide the required
precision for the task, or the degree of difficulty involved in placing the
lift properly, or the consequences of placing the lift improperly.  The CO
did not emphasize the precision required to place the forklift properly.

14.  The FAA does not approve the carriers' maintenance procedures, and a
carrier has the right to change its maintenance procedures without FAA approval.

15.  American Airlines personnel removed the aft bulkhead's bolt and bushing
before removing the forward bulkhead attach fittings.  This permitted the
forward bulkhead to act as a pivot.  Any advertent or inadvertent loss of
forklift support to the engine and pylon assembly would produce an upward
movement at the aft bulkhead's upper flange and bring it into contact with
the wing clevis.

16.  American Airlines maintenance personnel did not report formally to their
maintenance engineering staff either their deviation from the removal sequence
contained in the ECO or the difficulties they had encountered in accomplishing
the ECO's procedures.

17.  American Airline's engineering personnel did not perform a thorough
evaluation of all aspects of the maintenance procedures before they formulated
the ECO.  The engineering and supervisory personnel did not monitor the
performance of the ECO to ensure either that it was being accomplished properly
or if their maintenance personnel were encountering unforeseen difficulties in
performing the assigned tasks.

18.  The nine situations in which damage was sustained and cracks were found on
the upper flange were limited to those operations wherein the engine and pylon
assembly was supported by a forklift.

19.  On December 19, 1978, and Feb. 22, 1979, Continental Airlines maintenance
personnel damaged aft bulkhead upper flanges in a manner similar to the damage
noted on the accident aircraft.  The carrier classified the cause of the damage
as maintenance error.  Neither the air carrier nor the manufacturer interpreted
the regulation to require that it further investigate or report the damages to
the FAA.

20.  The original certification's fatigue-damage assessment was in conformance
with the existing requirements.

21.  The design of the stall warning system lacked sufficient redundancy; there
was only one stickshaker motor; and further, the design of the system did not
provide for crossover information to the left and right stall warning computers
from the applicable leading edge slat sensors on the opposite side of the
aircraft.

22.  The design of the leading edge slat system did not include positive
mechanical locking devices to prevent movement of the slats by external loads
following a failure of the primary controls.  Certification was based upon
acceptable flight characteristics with an asymmetrical leading edge slat
condition.

23.  At the time of DC-10 certification, the structural separation of an engine
pylon was not considered.  Thus, multiple failures of other systems resulting
from this single event was not considered.


Additional excerpts:

[design requirements for slats]
	"The motion on the flaps on opposite sides of the plane of symmetry
	must be synchronized unless the aircraft has safe characteristics with
	the flaps retracted on one side and extended on the other."

Since the left and right inboard slats are controlled by a single valve and
actuated by a common drum and the left and right outboard slats receive their
command from mechanically linked control valves which are "slaved" to the
inboard slats by the followup cable, the synchronization requirement was
satisfied.  However, since the cable drum actuating mechanisms of the left and
right outboard slats were independent of each other, the possibility existed
that one outboard slat might fail to respond to a commanded movement.
Therefore, the safe flight characteristics of the aircraft with asymmetrical
outboard slats were demonstrated by test flight.  These flight characteristics
were investigated within an airspeed range bounded by the limiting airspeed for
the takeoff slat positions--260 kts--and the stall warning speed; the flight
test did not investigate these characteristics under takeoff conditions.
In addition, a slat disagree warning light system was installed which, when
illuminated, indicated that the slat handle and slat position disagree, or
the slats are in transit, or the slats have been extended automatically.

The program engineer stated that the commanded slat position is held by trapped
fluid in the actuating cylinder, and that no consideration was given to an
alternate locking mechanism.  The slats' hydraulic lines and followup cables
were routed as close as possible to primary structure for protection; however,
routing them behind the wing's front spar was not considered because of
interference with other systems.

"The branch chief of the Reliability and Safety Engineering Organization of the
Douglas Aircraft Company described the failure mode and effects analysis (FMEA)
and fault analysis.  The witness indicated that the FMEA was a basic working
document in which rational failure modes were postulated and analyzed; vendors
and subcontractors were requested to perform similar analyses on equipment they
supplied to McDonnell-Douglas.  Previous design and service experience was
incorporated in the initial DC-10-10's FMEA's, and analyses were modified as
the design progressed.  The FMEA's were synthesized to make fault analyses,
which were system-oriented summary documents submitted to the FAA to satisfy 14
CFR 25.1309.  The FAA could have requested and could have reviewed the FMEA's.

The basic regulations under which the slats were certified did not require
accountability for multiple failures.  The slat fault analysis submitted to the
FAA listed 11 faults or failures, all of which were correctable by the
flightcrew.  However, one multiple failure--erroneous motion transmitted to
the right-hand outboard slats and an engine failure on the appropriate side--
was considered by McDonnell-Douglas in its FMEA.  The FMEA noted that the
"failure increases the amount of yaw but would be critical only under the most
adverse flight or takeoff conditions.  The probability of both failures
occurring is less than 1 x 10e-10 [a popular number with airframe
manufacturers!]."

[...]

"The December 1, 1978 revision of 14 CFR 25.571 retitled the regulation
"Damage-Tolerance and Fatigue Evaluation of Structure."  The fail-safe
evaluation must now include damage modes due to fatigue, corrosion, and
accidental damage.  According to the manufacturer, the consideration for
accidental damage was limited to damage which can be inflicted during routine
maintenance and aircraft servicing."

[...]

"Because of the designed redundancy in the aircraft's hydraulic and electrical
systems, the losses of those systems powered by the No. 1 engine should not have
affected the crew's ability to control the aircraft.  However, as the pylon
separated from the aircraft, the forward bulkhead contacted and severed
four other hydraulic lines and two cables which were routed through the wing
leading edge forward of the bulkhead.  These hydraulic lines were the operating
lines from the leading edge slat control valve, which was located inboard of
the pylon, and the actuating cylinders, which extend and retract the outboard
leading edge slats.  Two of the lines were connected to the No. 1 hydraulic
system and two were connected to the No. 3 system, thus providing the
redundancy to cope with a single hydraulic system failure.  The cables which
were severed provided feedback of the leading edge slat position so that the
control valve would be nulled when slat position agreed with position commanded
by the cockpit control.

The severing of the hydraulic lines in the leading edge of the left wing could
have resulted in the eventual loss of No. 3 hydraulic system because of fluid
depletion.  However, even at the most rapid rate of leakage possible, the system
would have operated throughout the flight.  The extended No. 3 spoiler panel on
the right wing, which was operated by the No. 3 hydraulic system, confirmed that
this hydraulic system was operating.  Since two of the three hydraulic systems
were operative, the Safety Board concludes that, except for the No. 2 and No. 4
spoiler panels on both wings which were powered by the No. 1 hydraulic systems,
all flight controls were operating.  Therefore, except for the significant
effect that the severing of the No. 3 hydraulic system's lines had on the left
leading edge slat system, the fluid leak did not play a role in the accident.

During takeoff, as with any normal takeoff, the leading edge slats were
extended to provide increased aerodynamic lift on the wings .  When the slats
are extended and the control valve is nulled, hydraulic fluid is trapped in the
actuating cylinder and operating lines.  The incompressiblity of this fluid
reacts against any external air loads and holds the slats extended.  This is
the only lock provided by the design.  Thus, when the lines were severed and
the trapped hydraulic fluid was lost, air loads forced the left outboard slats
to retract.  While other failures were not critical, the uncommanded movement
of these leading edge slats had a profound effect on the aerodynamic performance
and controllability of the aircraft.  With the left outboard slats retracted
and all others extended, the lift of the left wing was reduced and the airspeed
at which that wing would stall was increased.  The simulator tests showed that
even with the loss of the No. 2 and No. 4 spoilers, sufficient lateral control
was available from the ailerons and other spoilers to offset the asymmetric
lift caused by left slat retraction at airspeeds above that at which the wing
would stall.  However, the stall speed for the left wing increased to 159 KIAS.

[...]

The Safety Board is also concerned that the designs of the flight control,
hydraulic, and electrical systems in the DC-10 aircraft were such that all
were affected by the pylon separation to the extent that the crew was unable to
ascertain the measures needed to maintain control of the aircraft.

The airworthiness regulations in effect when the DC-10 was certificated were
augmented by a Special Condition, the provisions of which had to be met before
the aircraft's fully powered control system would be certificated.
The Special Condition required that the aircraft be capable of continued
flight and of being landed safely after failure of the flight control system,
including lift devices.  These capabilities must be demonstrated by analysis
or test, or both.  However, the Special Condition, as it applied to the slat
control system, was consistent with the basic airworthiness regulations in
effect at the time.  The basic airworthiness regulations specified requirements
for wing flap asymmetry only and did not include specific consideration of
other lift devices.  Because the leading edge slat design did not contain any
novel or unusual features, it was certificated under the basic regulation.  The
flap control requirements for symmetry and synchronization were applied to and
satisfied by the slat system design.  Since a malfunction of the slat actuating
system could disrupt the operation of an outboard slat segment, a fault analysis
was conducted to explore the probability and effects of both an uncommanded
movement of the outboard slats and the failure of the outboard slats to respond
to a commanded movement.  The fault analysis concluded that the aircraft could
be flown safely with this asymmetry.

Other aircraft designs include positive mechanical locking devices to prevent
movement of slats by external loads following a primary failure.  The DC-10
design did not include such a feature nor was it deemed necessary, since
compliance with the regulations was based upon analysis of those failure modes
which could result in asymmetrical positioning of the leading edge devices and
a demonstration that sufficient lateral control was available to compensate for
the asymmetrical conditions throughout the aircraft's flight envelope.  The
flight tests conducted to evaluate the controllability of the aircraft were
limited to a minimum airspeed compatible with stall-warning activation
predicated upon the slat-retracted configuration.

Newsgroups: sci.aeronautics.airliners
From: rdd@cactus.org (Robert Dorsett)
Subject: Re: hydraulic problems with DC-10's??
Date: Wed, 25 Nov 92 06:58:52 CST

In article <airliners.1992.32@ohare.Chicago.COM> kls@ohare.Chicago.COM (Karl Swartz) writes:
>In article <airliners.1992.30@ohare.Chicago.COM> weiss@curtiss.SEAS.UCLA.EDU (Michael Weiss) writes:
>>I have a hard time believing that an intact hydraulic system would have
>>prevented AA191 from crashing.  Let's face it, a wing-mounted engine falling
>>off produces such a rediculous unbalance that even full aileron wouldn't be
>>able to counter it.
>
>I don't see that ailerons have much to do with it -- the biggest
>effect would be a substantial yaw, which would require rudder input.

In the NTSB report on the DC-10 crash, a considerable amount of both yaw
and rudder were necessary to regain level flight, in the simulator tests--
80% right rudder and 70% right-wing-down aileron; roll angles didn't
exceed 30 degrees before recovery.

Normally, given asymmetric thrust, you bank into the good engine(s): rudder's
normally used to augment the ailerons as necessary to control sideslip.




>Having lots of altitude and airspeed to work with is certainly quite
>helpful, but isn't a requirement.  A few years ago a Piedmont 737-200
>lost #2 immediately after takeoff from O'Hare.  The pilots promptly
>declared an emergency, turned around, and landed several minutes later
>on another runway.  They didn't even realize that the engine had
>litterally fallen off until the got off he plane and looked.

There are actually two issues at work, here: one is the *power* lost by
the engine.  To maintain level flight, the power required for flight must
equal the power available.  If the power available is less, one will start
to descend; if it's a lot less, one will descend faster.  The real issue is
just power: it has little to do with where the failure was: losing two
of three engines on a 727 at MTOW means you'll go down, too.

The second issue is the moment produced by the combination of the "dead"
engine (with its drag) and the "good" engines.  This is generally a minimal
issue, assuming the airspeed is there, and the pilot applies correct
technique.  Most transport aircraft can fly with all engines out on one side,
although I do not know if this is an explicit regulatory requirement.  As
long as the inherent longitudinal stability of the airplane (contributed
by the vertical stabilizer, rudder, wings, and fuselage) is sufficient to
overcome the yawing moment, the airplane can be controlled.  So *correcting*
for a lost engine is a near-instantaneous correction, applied by the pilot,
needing no altitude reserve.


During the El Al discussion on sci.aero, rec.av, and rec.travel.air, there
seemed to be considerable confusion between the role each factor took.





---
Robert Dorsett
rdd@cactus.org
...cs.utexas.edu!cactus.org!rdd

Newsgroups: sci.aeronautics.airliners
From: Keith Barr <barrk@ucsu.Colorado.EDU>
Subject: Re: hydraulic problems with DC-10s??
Date: 04 Dec 92 22:30:39 PST

Subject: Re: hydraulic problems with DC-10's??
Robert Dorsett Says:
> Normally, given asymmetric thrust, you bank into the good engine(s): rudder's
> normally used to augment the ailerons as necessary to control sideslip.

Actually, you have this backwards.  Rudder is used to control the yaw,
and by controlling the yaw you introduce some sideslip that should be
counteracted by banking into the good engine (raise the dead is the way
I was tought to remember that :^)

The way this works is as follows....we will have to make due with ASCII
graphics:

Normal Flight (Multi-Engine, Both turning)
     Left thrust  Right thrust
             |     |
             |  A  |
       ------X--A--X------
                A
                A
              --A--
                |
                |
                |
                |
               Drag

Engine Out Flight (no correction)
        left thrust
             |
             |  A
       ------X--A--X------
                A          CW Moment
                A            |_
              --A--
                |
                |
                |
                |
               Drag

Engine Out Flight (Yaw (moment) correction)
       left thrust
             |
             |  A
       ------X--A--X------
                A
                A
              --A--===>Rudder Force to counteract rotation
                |
                |                 Now you can see we have fixed the
                |                 Rotation with rudder, but we have an
                |                 unbalanced vector diagram, so the aircraft
               Drag               will sideslip to the right

By raising the dead engine we tilt the lift vector to the left which balances
the force from the rudder.

> The second issue is the moment produced by the combination of the "dead"
> engine (with its drag) and the "good" engines.  This is generally a minimal
> issue, assuming the airspeed is there, and the pilot applies correct
> technique.  Most transport aircraft can fly with all engines out on one side,
> although I do not know if this is an explicit regulatory requirement.  As
> long as the inherent longitudinal stability of the airplane (contributed
> by the vertical stabilizer, rudder, wings, and fuselage) is sufficient to
> overcome the yawing moment, the airplane can be controlled.  So *correcting*
> for a lost engine is a near-instantaneous correction, applied by the pilot,
> needing no altitude reserve.

Correct, but here is an added explanation for those who care:
There is really only one concern of the pilot in an engine out situation, that
is airspeed.  The pilot, if he has done an appropriate preflight, will know
whether he/she is able to climb on one engine out, so that is not a suprise.
The biggest problem with an engine out is loss of control.  This airspeed,
called Vmc (Velocity Minimum Controllable) is the speed at which the rudder
doesn't have enough air flowing over it to create enough force to counteract
the moment from the good/dead engine.  As long as you are above this speed,
you should be controllable (ignoring the fact that one wing may stall if
the slat comes up, but I am not talking about that case in particular).

On the same thread, but different argument...
Michael Weiss writes:
>I have a hard time believing that an intact hydraulic system would have
>prevented AA191 from crashing.  Let's face it, a wing-mounted engine falling
>off produces such a rediculous unbalance that even full aileron wouldn't be
>able to counter it.

>After the third post with this answer, I figure it's time to clarify my
>statement.  I am referring to the unbalance of WEIGHT, not THRUST.  Nonetheless
>I suppose we should go on...

The change in weight from a lost engine is minimal.  A fully loaded DC-10-30
weighs 572,000 pounds.  A GE CF6-50C2B weighs only 8,731 pounds.  This means
that in normal flight each wing needs to support 286,000 pounds.  If each
wing supports the weight of its engine, now the left wing only needs to
create 277,269 pounds of lift, a 3.05% decrease.  I would imagine that
ailerons easily can create a 3.05% increase in lift per side.

References:  Aviation Week and Space Technology 3/16/92 p. 102
             Illustrated Encyclopedia of Commercial Aircraft pp 148-157
 _____________________________           _____
| Keith Barr                  \           \ K \__      _____
| barr@ncar.ucar.edu           \___________\   \/_______\___\_____________
| Comm/AS&MEL/Inst/IGI         /           < /_/   .....................  `-.
|_____________________________/             `-----------,----,--------------'
When you think how well basic appliances work, it's   _/____/
hard to believe anyone ever gets on an airplane.--Calvin

Newsgroups: sci.aeronautics.airliners
From: Robert Dorsett <rdd@rascal.ics.utexas.edu>
Subject: Re: hydraulic problems with DC-10's??
Date: 10 Dec 92 00:52:08 PST

Before starting: the left pylon assembly weight, btw, was 13,477 lbs, from
the accident report.  A whole bunch of figures had been floating around...


In <airliners.1992.106@ohare.Chicago.COM> Michael Weiss writes:

>In any case, my point is that there would have been a severe weight unbalance
>between the wings, and I have doubts that it could have been countered by the
>ailerons.  The whole reason that there was a negative roll moment was that the
>left wing STALLED, not that it lost lift directly from the retracting slats.
>I'm still not convinced that even WITH the slats extended it could have been
>prevented.

Allow me to throw in my $0.02 worth.

1.  A slat increases the maximum effective lift coefficient for a wing section.
How this is done is irrelevant to this discussion: the result is that the
lift coefficient goes up.  Slats permit the wing to produce a greater lift at
slower airspeeds, i.e., they drive the stall speed down.  When used with
trailing edge flaps, they offer even better lift characteristics, and improve
handling characteristics.

2.  If we take away the slats, then the maximum lift coefficient goes down.
By definition.  This means the stall speed goes up for the resulting
configuration.  By definition.

3.  The accepted procedure was to climb at V2 until 800' AGL, then to lower
the nose and accelerate.

For a normal, undamaged aircraft, at 379,000 lbs, V2 was 153 knots.

In the damaged aircraft, the minimum controllable airspeed, with a 4 degree
left bank, into the missing engine, was 159 knots.

Therefore, if the crew were to fly a standard engine-out profile, at 153
knots, they would have been beneath the minimum controllable airspeed for
the damaged aircraft (159 knots).

During the investigation, the NTSB asked 13 qualified pilots to fly various
takeoff profiles.  70 takeoff simulations were flown.  All crashed the
airplane when flying the crash profile.  Several pilots, when left to their
own devices, and with extensive knowledge of the events, managed to control
the airplane, nonetheless, by recognizing the initial roll and applying full
opposite aileron and significant rudder, and lowering the nose to gain air-
speed.  All pilots who received appropriate feedback, via a functioning
stickshaker, and who increased their airspeed to stay above the stickshaker
value--168 knots--saved the airplane.



I really fail to see what the problem is, here.  The engine fell off after
V1.  This didn't affect the aerodynamic characteristics of the wing itself:
it became a control problem.  It also killed the electrical system driving
the captain's stick-shaker, and killed a hydraulic system.  The latter
caused the slats to retract within 20 seconds of failure.

The slat retraction DID affect the wing: it then became both a control and
aerodynamic problem.  Exercising established control practices in an
unknown aerodynamic regime crashed the airplane (I'd love to know whether
this went into Airbus's "pilot error" database :-)).  Had the slats remained
down, the airplane would have survived the engine failure, even with the
failure of the stall warning system.  Other airframe manufacturers have
manual locking mechanisms for their slat jackscrews.  McDonnell Douglas
relied on hydraulic pressure to hold it all together.

Incidentally, this problem wasn't corrected: the SUX DC-10 also experienced
extension of its slats after it lost all its hydraulics.

I'd suggest you obtain a copy of the accident report (NTSB-AAR-79-17), and
look it over, closely.  It has more than enough data for back-of-the-
envelope calculations.  Nothing in it suggests that weight or moments
following engine separation played a significant role.


Lastly, I'd note that there was SIGNIFICANT public and industry concern
about the DC-10's safety after this crash: the FAA's extraordinary grounding
of the airplane, inappropriate though it may have been, is testimony to
that.  All of the manufacturers had something to contribute, and a great
deal of manpower was invested in finding the cause.  There was REAL concern
that the airplane wasn't airworthy, even by FAA's standards.  Every analysis
or comment I've ever seen on this crash has concentrated on the slat retrac-
tion being the proximal cause for the crash.  I've never seen the weight
issue raised.  If you have "hard" evidence that it HAS been, some references
would be useful, since it's not a well-publicised theory.  If you're
basing your comments on classroom experience, as I believe you indicated,
it might be a worthwhile learning exercise to raise it in class, or print
this discussion and privately  discuss it with your professor: but be sure
to let us know the outcome.







--
Robert Dorsett
Internet: rdd@rascal.ics.utexas.edu
UUCP: ...cs.utexas.edu!rascal.ics.utexas.edu!rdd

Newsgroups: sci.aeronautics.airliners
From: barr@ash.mmm.ucar.EDU (Keith Barr)
Subject: Re: hydraulic problems with DC-10s??
Date: 10 Dec 92 00:52:10 PST

greg@octopus.dpsi.com (Gregory R. Travis) writes:
> BTW, just to be pedantic:  The wings do not each contribute exactly
> 50% of the total lift.  Remember that that fuselage itself contributes
> a SUBSTANTIAL amount of lift at cruise as do the horizontal stabilizer
> surfaces (in certain flight regimes!).

What flight regimes might those be?  Unstable flight, as in the F-16?

Actually, in most aircraft the horizontal stabilizer is downlifting, so
the wings have to create more lift, and the body contributes to the
pitching moment, but contributes very little lift (unless we are talking
about the B-2).

For the horizontal stabilizer to lift up, the CG would have to behind the
Center of lift, which is not usually allowed.  I would bet a dollar that
the DC-10 has a down lifting tail, although I don't know for sure.

If you want references for either of these points, I recommend that you
look at Etkin's book on stability (an engineering text I used in my
aircraft design class that would explain in painful detail why you need
the CG in front of the Center of Lift), and you might check out K.D.
Wood's text on aircraft design for discussions about pitching moment and
lift created by the fuselage.

(is it just me, or is this thread becoming less and less appropriate for
this newsgroup?)
 _____________________________           _____
| Keith Barr                  \           \ K \__      _____
| barr@ncar.ucar.edu           \___________\   \/_______\___\_____________
| Comm/AS&MEL/Inst/IGI         /           < /_/   .....................  `-.
|_____________________________/             `-----------,----,--------------'
When you think how well basic appliances work, it's   _/____/
hard to believe anyone ever gets on an airplane.--Calvin

Newsgroups: sci.aeronautics.airliners
From: rdd@cactus.org (Robert Dorsett)
Subject: Slat extension locks
Date: 29 Jun 93 09:22:55 PDT

In previous DC-10 discussions (last year, mainly), I erroneously referred
to the Boeing use of "jackscrews" to lock leading edge devices.  This is
incorrect.  Jackscrews are used to some extent for trailing edge extension,
but aren't used for leading edge devices in any airplanes I'm familiar with.

I recently learned that the locking mechanism for the LED's is to trap
hydraulic fluid downstream of the actuator.  The locking mechanism is located
in the extension piston itself, and may not be opened again except by more
hydraulic pressure, during the retract cycle.

Thus, if the hydraulic system is lost, the device itself will remain firmly
wedged extended, with a small quantity of hydraulic fluid present in the
sealed piston.  Probably held more firmly than with hydraulic pressure
present.

I'm told that this system is so reliable that it's caused many a problem for
maintenance-type people once an actuator itself fails: there's no way to
retract the slats on the ground.  Boeing apparently sells a little hand-
pump to permit the fluid to be removed, but I'm told of one incident which
involved the use of a hacksaw. :-)

Sorry for any confusion, for those who hang on my every word. :-)


Egomaniacally,

---
Robert Dorsett
rdd@cactus.org
...cs.utexas.edu!cactus.org!rdd

Newsgroups: sci.aeronautics.airliners
From: kbarr@nyx10.cs.du.edu (Keith Barr)
Subject: Re: The Scoop on the A330 Accident
Date: 20 Jul 94 02:13:02

In article <airliners.1994.1441@ohare.Chicago.COM>,  <dalden@legal.com> wrote:
>Thank you, Peter, for the translation of the A330 accident.  One point
>comes to mind:  If Vmc is the minimum speed at which directional control
>can be maintained when one engine is developing zero thrust, the other
>is developing full thrust and the CG is at its most rearward limit [the
>configuration of the A330], how was directional control maintained
>between 18-28 kts below Vmc?

Vmc is not a fixed airspeed.  The one displayed on your airspeed indicator
by a red line (not to be confused with the red line indicating Vne) is
generally the one that is the highest.  Vmc is changed by aircraft loading
(which changes the moment arm of the rudder, so an aft CG is the worst),
by changes in altitude, by changes in aircraft attitude, and by changes in
power output from the good engine (idle the good one, and Vmc basically
goes away).

In flight, a pilot really only has control of the last two items mentioned
above.  Changine power output is fairly obvious, so I will explain how
aircraft attitude can effect Vmc.

In an engine out situation, (we will use right engine out) we have the
following (simplified) situation aerodynamically:

                /\
        thrust |  |
          ^    |  |
          |    |  |
          _    |  |    _                /
   ______|_|___|  |___|_|______        /
  |____________|  |____________|      /   Aircraft movement
               |  |
               |  |
               |  |
               |  |
             __|  |__
            |___\/___| -> rudder


Summing moments, we find that the clockwise moment created by the thrust is
balanced by the counter-clockwise moment created by the rudder.  If we sum
forces in the lateral direction, we find that the rudder has now created
an unbalanced force which causes the aircraft to move towards the dead
engine, which effectively reduces the angle of attack on the vertical
stabilizer.

By raising the dead engine, we "tilt" the lift vector of the wing to the
left, which creates a horizontal component of lift to balance the side-slip
condition created by the rudder.  If we continue to increase the bank
angle, we then induce a slip in the other direction, and start increasing
the angle of attack seen by the vertical stabilizer, which increases its
effectiveness, thus lowering Vmc.

Normal procedure after an engine failure is to raise the dead engine about
5 degrees, which counter-acts the side-slip condition, and lowers Vmc
somewhat.

As a side note, when I was working on my multi-commercial certificate, I
had to demonstrate approach to and recovery from Vmc.  It is usually
pretty apparent that you are at Vmc because even though you have full
rudder in, the nose of the aircraft starts to yaw towards the dead engine.
to fix the situation, you immediately decrease power on the good engine,
lower the nose, and as the airspeed comes above red line, you start
increasing power on the good engine again.  This was my least favorite
demonstration in the multi-engine aircraft. (Emergency descents were the
most fun--idle the engines and dive for the ground! :^)
 _____________________________           _____
| Keith Barr                  \           \   \__      _____
| barr@netcom.com              \___________\   \/_______\___\_____________
| Commercial/AS&MEL/Inst/A&IGI /           ( /_/   .....................  `-.
|_____________________________/             `-----------,----,--------------'
                                                      _/____/

Newsgroups: sci.aeronautics.airliners
From: rdd@netcom.com (Robert Dorsett)
Subject: Re: A positive aspect of the DC-10?
Date: 13 Feb 95 01:44:21

In article <airliners.1995.135@ohare.Chicago.COM> rna@gsb-pound.stanford.edu writes:
>I had heard about a similar incident at Minneapolis, between two DC-10s.
>
>Apparently the pilot who was taking off had received special training
>about just this feature of the 10, and rotated early, again clearing
>the aircraft in his way.
>
>Followups to sci.aeronautics.airliners.  I'd like to hear more about this
>aspect of the DC-10.  It's not generally thought to be a very safe
>airplane, so hearing more about it would be interesting.

A FedEx mechanic told me that since DC-10 the ORD disaster in 1979, reference
speeds for takeoff were pushed forward a few knots, resulting in
greater airspeed protection should there be another asymmetric slat retrac-
tion following engine failure near V2.  This results in a shallower takeoff
angle, and, presumably, a longer roll-out (note that contrary to what many
pilots think, there were no structural enhancements or changes to how the
airplane or its systems work as a result of that crash).

If the crew chooses not to exercise this protection (from news footage of
KC-10s taking off for the Gulf a couple months ago, I assume the military
doesn't), it gives the airplane a little bit of kinetic energy which can
be traded for altitude or maneuvering capability.

Very little about this bird gives me any peace of mind.


>>to lift off with less runway than necessary.  That characteristic actually
>>avoided a runway collision in Detroit several years ago.  A 727 happen to
>>be crossing the runway in front of a DC-10 approaching take-off speed.  The
>>pilot of the 10 remembered this fact and rotated the nose and managed to
>>clear the 727 by about 75 ft.  Not much of a margin but the captain was
>>thankful about the feature.