Central Air Safety An Investigation Gone Right

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April 2000 – US AIRWAVES 9
John Cox (PHL)
Vice Chairman, ALPA Executive Air Safety Committee
Central Air Safety
“ . . . all operators
of the Airbus
318/319/320/321
will be told what
we learned and
how to avoid or
contend with the
problems that one
of our flight crews
experienced.”
An Investigation Gone Right
All too often, the reports we hear are
about the story of an incident and an
investigation gone wrong. Occasionally,
there is a story about an incident where the
investigation goes the way it should. In January,
an event occurred in Charlotte that started an
investigation where cooperation, diligence, and
hard work came together to produce a better
understanding about the inter-workings of our
Airbus 319/320s. As a result, all operators of
the Airbus 318/319/320/321 will be told what
we learned and how to avoid or contend with the
problems that one of our flight crews experienced.
In mid-January, a low-pressure system reduced
the visibility in Charlotte to less than one
mile with snow falling. As the snow accumulated,
runway plowing caused a single runway to
be used. Air traffic control vectored one of our
A319s for the ILS approach to Runway 36R.
This A319 was one of a large number of
inbound aircraft. Because there was only one
runway in use, when the Airbus received clearance
for the ILS approach, they were over 25
miles from the runway threshold. In level flight,
flying 160 knots at 3600 feet, the Captain armed
the approach mode and armed the second autopilot
in accordance with procedure. Soon afterwards,
they approached the localizer and the
Airbus turned to intercept it. As they tracked
the localizer, all appeared normal.
As they closed to 22 miles from the runway,
the airplane pitched up abruptly. The crew
realized that the airspeed had deteriorated below
135 knots. Quickly, the Captain disengaged
the autopilot and autothrust systems. As
expected, the A319 responded normally to the
manual inputs made by the Captain. They descended
back to 3,600 feet and accelerated
back to 160 knots. What just happened? Why
did it occur? Would it happen again?
After reengaging the autopilot and autothrust,
the airplane flew a normal coupled approach
and auto-landing. Arriving at the gate the Captain
entered the pitch event into the maintenance
logbook. As one would expect, the
outbound flight canceled.
First indications were that an angle of attack
sensor provided incorrect information, and that
caused the pitch up. Later, upon further analysis,
this did not prove to be correct. The crew
contacted the Company and the ALPA Central
Air Safety Committee.
After some initial conversations with the
Fleet Manager, Captain Bob Skinner, we realized
that there were several unanswered questions
and very similar levels of concern. This
was a significant inflight event and there was
not a good explanation of the cause.
We decided that this required much more
investigation. A call to our Airbus avionicsengineering
experts in Tampa verified the de10
US AIRWAVES – April 2000
Central Air Safety
tails of the event. As we studied the flight data
recorder, several anomalies appeared. We began
to ask specific questions of Airbus to help
us understand what happened.
A conference call followed with the Airbus
engineers at the factory in Toulouse. They explained
what they saw in the flight data recorder
data. At the conclusion of the call, there were
still many unanswered questions. We discussed
using the engineering simulator to recreate the
event. Airbus concurred, and they set up the
time and the needed experts for the tests. After
a short debate, we decided that it would be
prudent for a couple of us to attend the tests.
Just before leaving for Toulouse, we were
able to contact ALPA Safety representatives at
other airlines that operate the Airbus and ask if
they were aware of any similar events. Surprisingly,
the answer came back that some of the
maintenance engineers were aware, but the pilots
were not.
Two days later, we arrived in Toulouse and
met with the Airbus engineers in person. Over
the next two days, we agreed on the conditions
that we would use in the simulator. Additionally,
we agreed that the participants in a postsimulator
meeting would decide on future action.
The stage was set to not only understand
the event but to take newly learned information
and distribute it to other operators.
Early in the morning, we met at the engineering
simulator. Along with the engineers was a
pilot from the Flight Testing Department. The
technicians loaded the data into the simulator,
and we began our tests. As expected, the simulator
followed the flight path of the event airplane.
It began to pitch up 22 miles from the
runway threshold just as the event airplane had.
The flight data recorder had recorded a glide
slope signal prior to the event. As the A319
tracked the localizer, all the conditions were
armed for a glide slope intercept. This would
have been normal except for the large scallop in
the glide slope signal that occurred causing the
flight management guidance computer to believe
that the aircraft was approaching the glide
slope. It then switched into glide slope ‘*’
(capture) mode. The scallop was very quick so
that the computer believed it was below a valid
glide slope and began to climb. This explained
the pitch-up and the quick rate of the pitch-up
because glide slope * can command up to three
times the normal pitch rate to capture the glide
slope. In addition, we then understood the
airspeed decay. It is normal for the Airbus to
“ The event was
the result of the
airplane performing
exactly as
designed. Pilot
intervention was
appropriate and
necessary. ”
trade airspeed for altitude in an effort to capture
the glide slope. We also learned that the
airplane remains within its protected flight envelope.
There is no danger of a stall. (You
cannot stall an Airbus when it is in normal law.)
The event was the result of the airplane performing
exactly as designed. Pilot intervention
was appropriate and necessary. This condition
was not unique to the Airbus: Other airplanes
have tracked false localizers or invalid glide
slopes. What was significant was the expectation
of the flight crew did not match the flight
path of the airplane. The pilots did not expect
the airplane to pitch-up, and they did not expect
the airspeed to decay appreciably.
After understanding what happened and why
it happened, we agreed that this information
should be sent to all Airbus pilots. Airbus
agreed to send a notice to all operators about
false glide slope interceptions. US Airways
created a Flight Information Letter for all Airbus
pilots. This way the information about the
consequences of a false glide slope capture
would be known and the appropriate pilot intervention
could occur earlier.
Airbus agreed to evaluate the design of the
logic for glide slope capture to reduce the
possibility of attempting to capture a false signal.
There are improvements that have been
made to the A330/340 and that logic improvement
may be usable in the A320 family.
While some follow-up work remains, the
majority of the investigation is complete. In
less than one month we learned of an event,
analyzed it, met with the Company about it, met
with Airbus about it, agreed on a plan to improve
pilot information worldwide about it, and helped
draft the flight information letter for US Airways
Airbus pilots, which then was distributed
promptly.
Sometimes an investigation goes right. This
one was the first time that we had seen a noteworthy
issue occur on the Airbus since we
began service in November 1999. The Company
agreed with our assessment and joined us
in the investigation. Airbus agreed with us and
joined us. Cooperation led to a quick resolution.
When it comes to safety and cooperation,
diligence and hard work is in everyone’s interest.
April 2000 – US AIRWAVES 11
Central Air Safety
In September 1989, one of our B-737-400s
performed a rejected takeoff in New York. It
resulted in an accident. I worked as the ALPA
representative on the powerplant group. After
the field phase was complete, Captain Bill
Sorbie, then-Central Air Safety Committee
Chairman, asked me to write an article for US
AIRWAVES about the investigation. That first
article began my regular contribution to US
AIRWAVES. It is now over 10 years later and
this is my last regular article.
In early March, ALPA’s Steering and Oversight
Committee selected me to the position of
Vice Chairman of ALPA’s Executive Air Safety
Committee. This is the number two position in
the safety structure for ALPA. This demanding
job deals with the safety concerns of 52 airlines
across two countries. There is considerable
diversity in the flight operations of these 52
airlines. They include small freight operations
in Canada to United Air Lines B-747s. It is
impossible do justice to this new job while
remaining as the AAA Chairman of the Central
Air Safety Committee. For that reason, I have
resigned as Chairman of your Central Air Safety
Committee.
The decision to take this new position was
not an easy one. It has been my privilege to
work with an outstanding group of professionals
while I was part of ALPA’s Safety Committee
at US Airways. The work was hard and the
hours long, but we made a difference. Safety at
our airline has improved. This advancement is
due, in part, to the work of many of ALPA’s
Central Air Safety Committee members. We
are industry leaders in effective cooperation
between the Association, the Company, and the
FAA.
Over the years, many other airlines have
visited us to see how we operate, how we are
organized, and how we take issues that are of
concern to our line pilots and improve the
safety of our flight operation. We led the
industry with our Altitude Awareness Program.
That is now expanded into the Aviation Safety
Action Partnership (ASAP), which will be the
standard of the airline industry soon. We led
the way in Flight Operation Quality Assurance
(FOQA). Again, that will be a standard soon.
We are much more standardized in our flight
operations than we were 10 years ago.
The list of our accomplishments is far too
long to enumerate here. Nevertheless, I remember
them all. It has been a privilege to be
a part of this. I have been glad to help our pilots
when there is a problem, incident or accident.
We have worked effectively with the NTSB and
FAA to ensure that our pilots received fair,
unbiased investigations.
The Central Air Safety Committee is working
as well as it ever has. The members are
involved in large numbers of projects. This
commitment will grow with our airline. International
operations are growing and so is the
safety responsibility to the crews that fly to
foreign countries. This is an area of focus for
this year. The effectiveness of the committee
in all of these projects will continue.
While my office will be in the ALPA building
in Herndon, Virginia, I will continue to be
available if needed. The relationship between
the ALPA Executive Air Safety Committee and
the US Airways Central Air Safety Committee
is very close. I expect that this will continue
and expand in the future.
Captain Terry McVenes has been appointed
as the interim Chairman of the Central Air
Safety Committee. Terry’s proven leadership
will serve to make the transition seamless. His
dedication is well established.
Ladies and gentlemen, thank you for the
opportunity of representing you in safety matters
for the last 14 years. I will continue to do
the best I can to improve safety in the aviation
industry for 51,000 airline pilots.
I sincerely appreciate the comments that
many of you have made about my US AIRWAVES
articles. I never claimed to be a writer.
After 10 years of writing articles regularly, I
have learned more about communication than I
ever expected to know.
I look forward to seeing you on the line.
Hopefully, I will get to fly a little more in this
new position.
A Change
“ Safety at our
airline has improved.
This
advancement is
due, in part, to the
work of many of
ALPA’s Central
Air Safety Committee
members.
We are industry
leaders in effective
cooperation
between the
Association, the
Company, and the
FAA. ”

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