Another 747 autopilot incident.

From:         rdd@cactus.org (Robert Dorsett)
Date:         25 Mar 93 00:08:38 PST
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The recent FLIGHT INTERNATIONAL report on a 747-100 missed-approach incident
mentioned an earlier one, taking place in 1989.  I looked it up: the following
is some interim coverage of that incident.  There don't seem to be 
overwhelming similarities.


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>From FLIGHT INTERNATIONAL, 18-24 July, 1990:

BA REPORT REVEALS LHR 747 OVERSHOOT FROM 75ft.

"A British Airways Boeing 747, involved in a low offset overshoot
incident at Heathrow last November,  came as low as 75ft (23m), a
confidental letter to BA 747 aircrew from the airline's chief 747
pilot has revealed.  The aircraft almost landed outside the airfield
boundary (FI, November 29, 1989).

"The 747 was inbound from Mauritius via Bahrain.  The flight engineer
and co-pilot were suffering from gastroenteritis and the copilot had
to rest in the cabin for three hours during the flight.

"The weather was bad and a Cat 3 landing was needed, the copilot was
new and had not completed his initial Cat 3 training detail, so the
captain obtained BA permission for the copilot to fly to all-weather
minima.  

"The aircraft, with A autopilot set, intercepted runway 27R ILS.  At
13 nm "Land" was selected and the B autopilot engaged.  The aircraft
captured altitude, then localizer at 10 nm, at which point the
engineer called a steady red warning on the B autopilot. The Flight
Data Recorder shows that shortly after, both autopilots were
disconnected and the aircraft flown manually in the "heading" mode.

"Dual Green/Flare Arm annunciators were not obtained from either
autopilot. To obtain these, both flight directors (DFs) must
annunciate Flare Arm. Each FD can only do this when the aircraft is
elow 1500 ft. radio altitude (R), the ILS localizer "on course"
conditions have been met for 5 seconds, and "Land" is selected.  B
autopilot was selected as the centerline was crossed so the
conditions were not met.  Had the aircraft been flown manually to
localizer alignment, then autopilots re-engaged, the aircraft would
have captured the ILS and achieved an autoland.

"Without the annunciations, autoland was impossible at at 1000' (300m)
R the crew should have abandoned the autoland and either gone around
or continued to Cat I minima.  They continued the approach but did
not change their minima.

"After deviating to the left, the 747 re-crossed the centreline at
577ft, heading 280 degrees and continued to deviate at an angle of
about 5 degrees.  At 500' the ILS deviation lights illuminated but
the aircraft was allowed to continue to deviate to beyond ILS
full-scale deflection and descended to 250' before the autopilots
were disconnected.  Some 17 seconds elapsed between the ILS deviation
lights coming on and autopilot disconnection.

"After the autopilots were disconnected the 747 continued to descend
for another 7 seconds until power was applied at 120ft and the
aircraft began to pitch up very slowly at less than  1 deg/sec (at
least 3 deg/sec is normal).  The minimum radio altitude recorded was
75 feet.

"The captain, who later resigned, subsequently made a successful auto
approach and manual landing using B autopilot.  In checks the A
autopilot was serviceable, the B system roll computer failed."