Newsgroups: sci.aeronautics.airliners
From: tristar500@aol.com (TriStar500)
Subject: Re: Details on recent PW-4xxx engine problems?
Date: 22 Jul 94 12:44:03

In article <airliners.1994.1455@ohare.Chicago.COM>, kls@ohare.Chicago.COM
(Karl Swartz) writes:

>The only problem I'm aware of with the PW4060 on the 767 was the in-
>flight reverser deployment which led to the Lauda Air crash outside
>Bangkok.

The engines also vibrate so bad that clamps and wiring harnesses are
self-destructing. This is on 767-300ER and A-310-300s. The ETOPs airplanes
are subject to a 'hardware' check almost everynight to look for damaged
clamps, hardware and wiring caused by the vibration.

RE: inflight deployment of thrust reversers.
The fix for this was the installation of 'sync locks'. These are
mechanical locks that prevent the TR sleeves from moving when they are not
commanded. In the old system, (prior to the sync locks) if an uncommanded
deployment of the reverser was sensed, hydraulic pressure was
automatically routed to the stow side of the thrust reverser actuators.
This would have been accompanied by the 'REV ISLN' EICAS message, which is
what the Lauda Air crew saw. Basically it was discovered that the crew
could deploy the reversers in flight if they moved the reverser handle
while the reversers where auto-stowing.

The sync locks were also installed on the 757 with PW2037 engines since
they use the same reverser system.

-----------------------------------
D.G. Davidson (TriStar500@aol.com)
Aviation Forum Host - America Online

Newsgroups: sci.aeronautics.airliners
From: rdd@rascal.ics.utexas.edu (Robert Dorsett)
Subject: Re: A320 braking methods
Date: 22 Oct 93 01:05:26 PDT

>> Wheel brakes are how the airplane is stopped.  Many people think the
>> thrust reversers play a large role: it's marginal, not affecting roll-out
>					^^^^^^^^^^
>> distance by more than 10-20%.
>
>	Robert, is that a quote or your opinion?  The reason I ask is
>	that this is the second time, I think, that I read this, and
>	the earlier time already I had wondered to myself:

Well, that specific figure was from Webb's _Fly the Wing_.

But let's just consider empirical evidence.  I'm an avid airplane-watcher.
737's at Mueller typically complete their turn-off within 25 seconds
after touch-down.  Figure a touch-down speed of 135 knots.  That's 228
feet per second.  Figure four seconds (typical) for selection and actuation of
thrust reversal--pilot's first responsibility upon landing is to keep the
nose pointed in the right direction; this takes time.  So does smoothly
spooling down, selecting reverse thrust, and advancing the throttles again.

By the point of selection, our airplane's traveled at most 912 feet (at
most, because wheel brakes are much more responsive, and would be applied
within two seconds after touchdown).  The engines must be cut down to idle,
and then accelerated.  That's another three to four seconds, and we're
probably down to around 90 knots, up to ~1500 feet of pavement, 7 to 10
seconds.

Probably takes another 7-10 to slow down to 40 knots.  But thrust reversers
are stowed at 65 knots, due to the danger of compressor stall and particle
ingestion.  So just with this back-of-the-envelope calculation, we're looking
at an interval of 30-40 knots that the thrust reversers can "help out" on.
How effective are they? Well, figure 30,000 lbs of thrust on a twin, landing
weight of 120,000 lbs.  Assume 80% power (I think Webb says 65%), at a 60%
efficiency.  That's a net yield of 16,800 lbs of thrust, or a deceleration
rate of 4.48 ft/sec^2.  Or 1.36 m/s^2, which is 80% of the brakes-only
antiskid threshold of 1.7 m/s^2 on the A320.  And you won't be getting
30,000 static lbs of power as a reference, since there's a power loss
as the airplane moves through the air.  Maybe 5% less, but we'll ignore
this.

But again, this is only in a 40-knot interval.  Distance traveled, assuming
uniform 3.4 m/s^2 deceleration during this interval, starting at 100 knots,
ending at 60 knots, is only around 807', or 6 seconds of time.  So out of a
landing roll of 3000' or so (regulatory runway landing distance of (1500' +
3000)/0.6 = 7500', so this is probably a bit high), the thrust reversers
are only responsible for around 50% of that 800', or 400', or 13%.  On a
wet runway, in this interval, the "contribution" figure MAY be a bit higher,
with inop antiskid.

Clearly, thrust reversers aren't HUGELY relevant.  Some reverse thrust is
going to be generated during the acceleration phase after door deployment,
so let's double it's contribution: 26%.  But this is all gravy: IF the
airplane lands where it's supposed to, we have a large amount of runway left
over for BRAKES-ONLY deceleration.  The thrust reversers will merely serve
to increase the margins, raising the "excess" pavement length by 26%.

No thrust reversers?  You still have 166% normal touchdown distance to
complete your brakes-only roll-out.  The penalty of NO thrust reversers
is, therefore, nonexistent, as far as the standards go.

This is all back-of-the-envelope, your mileage will vary.  But this is all
best-case, at sea level.  Throw in a hot day, high altitude situation, and
the influence of the thrust reversers will go way down.  The effectiveness
of braking won't change as much.


>	how many accidents that had planes overrun the runway, could
>	have been avoided with an additional "10 to 20" of ...
>	(you know what I mean: breaking power, runway, whatever..)

How many accidents  could have been avoided if 400% reverse power had been
available after the pilot touched down 70% down the runway?  Such questions
aren't very relevant.  Landing distances have generous amounts of error
built into them.   One might as well ask why we allow airplanes to brake
under their own power, and don't just use arresting gear and tailhooks to
stop the airplane within a few feet, no matter WHERE one lands on the
runway.  :-)

Thrust reversers aren't magic cure-alls.  They're meant to be used in
specified ways, and are subject to both mechanical limitations and the
laws of nature.

I think a good chunk of your reasoning (and similar thoughts have been
expressed on the net) is that thrust reversers make a HUGE difference in
roll-out.  They don't.  They LOOK awfully impressive from seat 35A, along
with the ground spoilers.  But take along your stop-watch on your next
flight.   :-)


>	my point is that I see no good reason to describe it as "marginal"
>	and wonder if it is a good idea to do so (no criticism intende
>	but rather plain puzzled)

I hope the above clarified things somewhat.



Cheers,


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

Newsgroups: sci.aeronautics.airliners
From: David Lednicer <dave@amiwest.com>
Subject: Early 737s
Date: 05 Oct 93 01:10:31 PDT

	The Boeing 737-100 (and -200) as originally flown, had thrust
reversers borrowd from the 727.  Because they were under the wing (as
opposed to behind the wing) it was found that they were VERY ineffective
(story has it that the aircraft would actually speed up when the reversers
deployed).  The reason for this problem was that the reverser, when
deployed, would create a high pressure region under the wing, and reduce
the downforce on the main wheels, thereby reducing braking effectiveness.
This problem was eventually fixed by extending the tailpipe aft of the
wing trailing edge, where it exited into a thrust reverser taken from the
Douglas DC-9.  I have pictures showing that quite a few 737s were
delivered to customers with the original thrust reverser.  Does anybody
know how many were delivered configured this way and when was the last one
finally retrofitted with the later thrust reverser?


				-David Lednicer

Newsgroups: sci.aeronautics.airliners
From: ehahn@fairlite.mitre.org (Ed Hahn)
Subject: Re: Reverse Thrust
Date: 22 Mar 94 09:52:38 PST

In article <airliners.1994.1026@orchard.Chicago.COM> "Donald A. Hazle"
<DAH@PSUVM.PSU.EDU> writes:

   Is reverse thrust used on some aircraft in flight to slow a decent?  I
   thought I had read in this newsgroup that reverse thrust was locked
   out during flight on most aircraft.  However, on a 1968 approach to
   Washington National (from northwest to southeast over the Potomac), the
   flight attendant announced; "the noise you hear are the engines running
   in reverse to control airspeed during our descent".
   The aircraft was a DC-9 an there was a higher amount of noise than normal
   coming from the rear.  I never heard this announced on any other flight.

   Don Hazle  Penn State University
----
For an airliner, reverse thrust is never used to slow an aircraft (in
flight, that is).  In fact, a Lauda Air B767 came apart in flight when
one of the thrust reversers deployed in flight accidentally over
Southeast Asia a few years back.  (The FAA has issued an Airworthiness
Directive about this.)

My conjecture regarding the noise in the DC9 is that the aircraft was flying
with full flaps, thus creating a lot of drag, in turn requiring a
fairly high power setting to maintain airspeed (not an unusual
situation on the River Visual approach to DCA).

In general, aircraft will use wing spoilers (i.e. mid-chord wing
panels that deploy upward - easily seen on B727s) for speed control.

The one exception is the F28/F100 (Fokker), which has a clamshell
spoiler at the tip of the rear fuselage (you can see the hinges
for the shells a few feet forward of the end of the fuselage).  The
wing actuated panels on these aircraft are LIFT DUMPERS, and are ONLY
actuated on the ground for braking purposes.  American Airlines,
USAir, and the new Midway are the primary US operators of this Dutch
twinjet.

Hope this helps, with a minimum of unintentional disinformation...
ed

Newsgroups: sci.aeronautics.airliners
From: drinkard@bcstec.ca.boeing.com (Terrell D. Drinkard)
Subject: Re: Lufthansa crash in Warsaw - Preliminary findings
Date: 22 Oct 93 01:05:03 PDT

In article <airliners.1993.655@ohare.chicago.com>,
Stefano Pagiola <spagiola@leland.Stanford.EDU> wrote:
>I'm not sure about thrust-reversing, but I remember Piedmont lost a
>737 at Charlotte some time ago when some combination of aquaplaning
>and floating in ground effect meant spoilers could not be deployed
>because releasing them requires the mainwheels to be firmly on the
>ground and to have begun turning.  Just as it makes sense (most of
>the time) to prevent spoiler deployment in flight, it probably would
>make sense to have similar safeguards to prevent thrust reverser
>deployment in flight.  Can anyone confirm whether/how its actually
>done?

[Quoting from the Airplane Systems Familiarization book - an in-house
Boeing publication]

Thrust reversers require the following to deploy:
1)  28VDC power available
2)  Engine fire switch in the normal position
3)  Airplane on ground (squat switches activated)
4)  Thrust lever in idle position
5)  Reverse thrust in the reverse idle detent position

Autospoilers require the following to deploy:
1)  Hydraulic pressure to the truck tilt indicators
2)  Both thrust levers at idle
3)  Both truck tilt sensors detect a no-tilt condition (a/p on ground)
4)  Speedbrake lever in the armed position

[End of quotes]

I can't imagine anyone using tire spin-up as an activation criterion for
autospoiler or thrust reverser operation.  Too much attention is paid to
the icy runway scenario (which is one reason that thrust reversers are
included even on the 737 where there is some concern about their
cost/benefit ratio).  Safety is of primary importance to Boeing, and I'm
quite sure, to Airbus as well.  No one benefits from an unsafe airplane.

My suggestion is to wait for more information before coming to any
conclusions about the contributing causes of the accident.  Pilot error
seems to be the primary cause given the weather.  This bears some
similarity to the Mokpo accident of a couple of months ago where the pilots
attempted three times to land in really bad weather.

Questions for Robert Dorsett:  Could the pilots high levels of experience
and presumed competence have contributed to a false sense of security
which led to an error in judgement?  If so, how can this be avoided in the
future?  Did the 'cocoon' effect of the A320 cockpit contribute to the
possible overconfidence?

Another idle thought:  The descriptions of the weather at Warsaw seem to
match the profile for microburst activity.  Did the pilots and controllers
not recognize this, or did I miss something?

--
Terry
drinkard@bcstec.boeing.com
"Anyone who thinks they can hold the company responsible for what I say has
more lawyers than sense."