Boeing Co 737-800, VH-VXD

Investigation number

200203641

Occurrence date

08/08/2002

Location

APOMA, (IFR)

Report release date

03/12/2002

Report status

Final

Investigation type

Occurrence Investigation

Investigation status

Completed

Aviation occurrence type

Air-ground-air

Occurrence category

Incident

Highest injury level

None

Safety Action Analysis Summary

Local safety action

The B737 operator amended controlled rest procedures to require
both crew members to be on duty when a change in level was
conducted.

ATSB safety action

The ATSB issued Safety Advisory Notice (SAN) 20010244 to the
aviation industry on 2 May 2002. That notice stated:

The Australian Transport Safety Bureau alerts all operators in
the transport industry, particularly those involved in
extended-hours operations, to the possibility of crew members
suffering sleep inertia and suggests that operators take steps to
mitigate the effects of sleep inertia. The steps should not include
subjecting employees to sleep deprivation.

The ATSB issued SAN20010245 to the Civil Aviation Safety
Authority on 15 April 2002. That notice stated:

The Australian Transport Safety Bureau suggests that the Civil
Aviation Safety Authority alert all aviation industry operators to
the possibility of sleep inertia impairing performance,
particularly that of flight and maintenance crews.

The ATSB also issued SAN20020035 to the Civil Aviation Safety
Authority on 15 April 2002. That notice stated:

The Australian Transport Safety Bureau suggests that the Civil
Aviation Safety Authority ensure that operators have strategies in
place to mitigate the effects of sleep inertia as part of their
fatigue management systems.

The co-pilot had less than nine hours of interrupted sleep
during the 48 hours preceding the incident. That small period of
sleep suggests that the co-pilot may have been fatigued at the time
of the incident despite feeling adequately rested. Fatigue may lead
to impaired physical and mental performance in people and may
explain why, when the controller requested confirmation of the
aircraft's level, the co-pilot relied on his memory rather than
performing the more demanding task of confirming the aircraft's
level by looking at the altitude indicator.

Within a short time of waking from the period of controlled
rest, the co-pilot had received a handover briefing and assumed
control of the aircraft. Despite reporting the correct level
(FL390) to the Bourke sector controller during a change of radio
frequency, the co-pilot subsequently reported an incorrect level
(FL370) a few minutes later with the APOMA position report.

It is likely that the co-pilot was suffering from the cumulative
effects of fatigue and sleep inertia that resulted in the incorrect
level being passed with the position report. The occurrence
highlights that an understanding of fatigue and how to manage it
are important defences to a human limitation.

Despite the aircraft being at flight levels that provided 2,000
ft vertical separation, the Bourke sector controller's provision of
mutual traffic information to both the co-pilot and the pilot of
the B747 was warranted. At that stage, the pilot reported
information provided to the controller indicated that a separation
standard was not being applied to the aircraft. The traffic
information would have assisted both crews to assess the potential
for conflict and would have provided a basis for pilot-initiated
avoiding action. Under the circumstances, the provision by the
controller of a safety alert that would have included a recommended
action to either turn or to climb/descend, as well as the provision
of traffic information, may have been a better option. That action
would have ensured that the pilots clearly understood that the
aircraft were in close proximity and at the same level, based on
the reports provided to the controller.

The co-pilot of a Boeing 737-800 (B737) en route from Perth to
Brisbane on air route T91 reported maintaining flight level (FL)
390. He later reported maintaining FL370 at APOMA, located 140 NM
north-northeast of Broken Hill, at 0501 EST. The Bourke sector
controller in the Melbourne Air Traffic Control Centre requested
the co-pilot to confirm the aircraft's level. The co-pilot replied
that the aircraft was at FL370. A Boeing 747 (B747) maintaining
FL370 was on a crossing route and estimated APOMA at 0503, two
minutes after the B737. To be separated, aircraft at the same level
on intersecting tracks required 15 minutes between their respective
intersection estimates. The controller issued traffic information
to the co-pilot of the B737 and to the crew of the B747.

At a subsequent position report the pilot in command (PIC) of
the B737 overheard the co-pilot report the aircraft's level as
FL370 and corrected the error. Later analysis of the flight data
recorder of the B737 confirmed that the aircraft had maintained
FL390. There was no infringement of separation standards.

The B737 operator had an approved procedure for the `controlled
rest' of flight crew members while remaining on the flight deck.
Controlled rest was recognised by the operator as `an effective
method of improving levels of crew alertness for critical phases of
flight'. There were a number of guidelines concerning the use of
the procedure, including:

It was not to be used on sectors of less than two hours
duration.
It was only to be used during the cruise phase of flight.
Periods of controlled rest were not to exceed 30 minutes per
crew member per sector.
An additional 10 minutes was required after the period of
controlled rest before a crew member resumed flight deck
duties.

At 0213, the B737 departed Perth and was climbed initially to
FL370. The flight plan advised an intention to change level to
FL390 by BEZZA, a position about 340 NM west of Leigh Creek. At
about 0405, the co-pilot requested and was approved by the PIC to
take a controlled rest. At 0416, the PIC requested and was approved
by the Melbourne Centre controller for the aircraft to climb to
FL390. At 0421, the PIC reported maintaining FL390 to the Melbourne
Centre controller. At about 0440, the co-pilot ceased the
controlled rest and was briefed by the PIC in the next five minutes
before assuming control of the aircraft. The briefing included the
level of the aircraft. The PIC then commenced a period of
controlled rest until about 0520. On initial contact with the
Bourke sector controller at 0458, the co-pilot reported that the
aircraft was maintaining FL390.

The roster for the 48-hour period preceding the incident
required the crew to commence work at about 1900 two days before
the incident and to operate a flight from Brisbane to Perth,
arriving in Perth at approximately 0120. They spent the remainder
of that day at their leisure prior to departing Perth for Brisbane
on the incident flight at 0213 the following morning. That
departure time required the crew to report for duty at
approximately 0100.

On the morning of the Brisbane to Perth flight the co-pilot
awoke at 0530 and had a 30-minute nap during that day. The co-pilot
slept for approximately 6.5 hours after arriving in Perth, had a
90-minute nap late that afternoon and 30 minutes of controlled rest
during the flight to Brisbane. Those periods of sleep accumulated
to about nine hours during the 48-hour period. The co-pilot later
reported that he felt rested prior to commencing the Perth to
Brisbane flight.

Fatigue is recognised as a primary cause of transport accidents
throughout the world as a result of reduced or impaired mental
and/or physical performance following inadequate rest.

One component of fatigue relevant to the transport industry is
sleep inertia. That phenomenon refers to the period of mental
dullness or sluggishness immediately after awakening. During a
period of sleep inertia people demonstrate the outward signs of
being awake but are not mentally awake. Research suggests that it
may take approximately 30 minutes after awakening for the effects
of sleep inertia to fully dissipate.

The co-pilot was newly rated on the B737-800 and reported that
he had found scanning the altitude indicator in that aircraft
series took longer and required additional conscious effort. The
co-pilot reported that when providing the aircraft's level, in
response to the Bourke sector controller's query, he had relied on
his memory of the information in the position report rather than
re-checking the altitude indicator on the flight instrument
display.

The Bourke sector controller twice requested confirmation of the
flight level from the co-pilot of the B737 and was advised on both
occasions that the level was FL370. At that stage, the controller
passed traffic information to the co-pilot about the B747 at FL370
on the crossing route. The controller also passed traffic
information on the B737 to the pilot of the B747. The co-pilot of
the B737 later reported that at that time he was unsure why the
controller had issued the traffic information as he could see the
B747 displayed on the B737's Traffic Alert and Collision Avoidance
System (TCAS) behind and 2,000 ft below his aircraft.

The Manual of Air Traffic Services (MATS) section covering
safety alerts (Section 5.1.13) included the following:

'A safety alert shall be issued to an aircraft when a controller
is aware the aircraft is in a situation which is considered to
place it in unsafe proximity to terrain, obstructions, or other
aircraft. The controller must remain vigilant for the development
of such situations and issue a safety alert when the situation is
recognised.

Conditions such as workload, traffic volume, the
quality/limitations of the radar system, and the available lead
time to react are factors in determining whether it is reasonable
for the controller to observe and recognise such situations.

The issuance of a safety alert is a first priority.

When a controller is aware that an aircraft is in unsafe
proximity to another aircraft, a safety alert shall be issued as
follows:

"(Callsign) TRAFFIC ALERT (position of traffic if time permits),
[SUGGEST] TURN LEFT / RIGHT (specific heading, if appropriate), and
/ or [SUGGEST] CLIMB / DESCEND (specific altitude if appropriate),
IMMEDIATELY".

When a safety alert is directed to traffic not receiving a
separation service, advice to turn or change level shall be
prefixed with the word SUGGEST'.

Aircraft Details

Manufacturer

The Boeing Company

Model

737

Registration

VH-VXD

Operation type

Air Transport High Capacity

Departure point

Perth, WA

Departure time

0213 hours EST

Destination

Brisbane, QLD

Damage

Nil