From: David Lednicer <email@example.com>
Subject: Nagoya CAL Crash
Date: 13 May 94 11:31:44
I have seen several posts now of info on this crash which have
been based upon newspaper reports. As has been borne out in the past,
reporters for newspapers are not very reliable subjects when it comes to
technical matters. On the other hand, Aviation Week & Space Technology
has proven to be rather trustworthy, and here is what they report in the
May 9, 1994 issue.
According to the preliminary CVR (Cockpit Voice Recorder) and DFDR
(Digital Flight Data Recorder) readings, at the time on approach that the
first officer engaged the auto-throttle, he also inadvertently activated the
TOGA (Take-Off and Go-Around) switch. "As a result, the aircraft's
auto-thrust and flight director reverted to automatic go-around mode and
the aircraft began to fly above the glide slope. The crew was apparently
startled and did not recognize that the TOGA had been activated. Chuang
[FO] applied nose down elevator in an effort to recapture the glide slope."
TOGA trims the stabilizer so as to pitch the aircraft's nose up and
the FO was moving the elevators so as to pitch the aircraft's nose down. At
this point the crew engaged the autopilot, which moved the stab to
maximum aircraft nose-up deflection. "Still, the crew continued to apply
nose-down inputs by overriding the autopilot as if trying to recapture
the glidepath for a landing. Such a tactic does not work because as soon
as the inputs are stopped the autopilot returns to flying its original
go-around flight path."
"A similar situtation to what CAL 140 experienced occured three
years ago on an Interflug A310. The crew ended up totally out of trim,
but they recovered." This is probably the incident outside Moscow that
we have seen postings here about.
"In such a configuration, since the stabilizer efficiency is
greater than that of the elevator, the aircraft could reach an abnormal
pitch-up angle leading to an airspeed decay." This is a quote from an
Airbus service bulletin quoted in the article.
"The stronger the force that the pilot puts on the flight control
column to activate the elevators, the faster the stabilizer trim will
respond to counteract the nose-down effort."
"At about 570 ft., both autopilots were disengaged. Airspeed was
129 kt. and pitch was 5.5 deg. Eight seconds later, at about 400 ft.,
the Airbus analysis concludes that the Alpha floor function was
triggered. Both engines accelerated normally to maximum thrust."
"Alpha floor is a safety function and is triggered before
stalling speed. "Now we have the moment that he has full stabilizer
trim, the power comes and brings his nose up," the captain said
[interviewed for the article]. "He cannot hold it with elevator. He has
to trim. If he doesn't trim, he has no chance. He has to trim the nose
forward, forward, forward [down]. It takes a few seconds. If he started
to trim, even in this position, he could have had a chance.""
"Coupled with the THS [stablizer] at maximum nose-up deflection,
the pitch attitude achieved at least 36 deg. - one Airbus source said 52
deg. [!] - 22 sec. after alpha floor activation. Flaps/slats were
retracted from 30/40 deg to 15/15 deg but the aircraft was in a stall
form which it could not recover." Estimates are that the airspeed had
decayed to 78 kts. in the end!
David Lednicer | "Applied Computational Fluid Dynamics"
Analytical Methods, Inc. | email: firstname.lastname@example.org
2133 152nd Ave NE | tel: (206) 643-9090
Redmond, WA 98052 USA | fax: (206) 746-1299