Short Bros Pty Ltd SD360-300, VH-SUM

Local safety action

As a result of this occurrence, the Australian Civil Aviation
Safety Authority (CASA) have taken the following actions:

1. Issued a direction on 5 July 2001, under the provision of Civil
   Aviation Regulation 38, to all Australian Certificate of
   Registration holders of Pratt and Whitney Canada PT6A turboprop
   powered aircraft, conducting fare-paying passenger operations. That
   direction required the operators to include in their System of
   Maintenance the following :
   
   
   
   a. 'Periodic in service S/G [starter-generator] field cleaning and
   resitance checks to be performed in accordance with the procedures
   detailed in TRW Lucas Maintenance Manual Number 23700, Revision 9
   at intervals not to exceed 300 hours S/G time in service; and
   
   
   
   b. Oil system monitoring of engines in service from which a S/G was
   removed to rectify a reported engine starting or electrical
   generation defect that was confirmed to be caused by the
   S/G.'
   
   
   
2. Sent an advisory letter on 5 July 2001, to all Certificate of
   Registration holders of Pratt and Whitney Canada PT6A turboprop
   powered aircraft. The letter advised the following:

'CASA investigation into reports of 17 in-flight shut downs
(IFSD) of PWC PT6A-60 series engines in the world fleet, 5 in
Australia, has determined those defects resulted from electrical
discharge damage (EDD) to the engine number 1 bearing. The
electrical current source is the engine starter-generator (S/G) TRW
Lucas models 23078 and 23085.

CASA has determined electrical current can flow to the engine
from the S/G armature output shaft through armature leakage or an
electrical short of the armature. The most probable cause of
armature leakage is an accumulation of brush dust. The TRW S/G
Maintenance Manual (M/M) 23700 includes periodic field cleaning and
resistance checks that will prevent brush dust build up and detect
a decrease in armature leakage resistance and a hard short.

Enclosed is further background information relating to this
subject.

Unfortunately, the aircraft manufacturer's maintenance schedules
for aircraft types known to have experienced PT6A EDD do not
reflect that detailed in the TRW Lucas M/M 23700. As such, the
aircraft manufacturer's instructions for continuing airworthiness
for those particular aircraft are deficient in respect of S/G
maintenance.

Whilst there is no evidence of EDD in PT6A models other than
PT6A-60 series engines incorporating a TRW Lucas S/G model 23078 or
23085, CASA recommends all PT6A operators carry out a review of
their elected aircraft maintenance schedule in consideration of
information learnt from the CASA investigation of the PT6A-60
series IFSD events.

As of this date, CASA has no evidence to support mandatory
action for PT6A powered aircraft operators other than those
conducting fare paying passenger operations in PT6A-60 powered
aircraft. CASA recommends that you review the enclosed information
and initiate any changes to your aircraft maintenance schedule as
you believe necessary to ensure the continued airworthiness of your
aircraft.'

CASA has also assisted the operator to introduce the following
local safety actions:

1. In conjunction with the aircraft manufacturer, carried out a
   bonding check to ensure that an appropriate electrical discharge
   path was available from the starter-generator.
2. Assisted the manufacturer in performing tests on
   starter-generators removed from service after 600 hours to
   determine any source of electrical leakage.
3. Installed a supplemental chip detector system on each engine
   accessory gearbox. Prior to and at the completion of each flight,
   the flight crew is required, to test the chip detector to determine
   that no metal has bridged the chip detector probes. Every 120 hours
   the accessory gearbox chip detector is to be removed and inspected.
   The chip detector probes are to be wiped and the results from the
   wipe are to be sent to a power plant repair facility for
   analysis.
4. Reduced the starter-generator overhaul period from 1,500 hours
   to 1,000 hours. At each 250 and 750 hour inspection the
   starter-generator is to be cleaned (brush dust removed) and the
   brushes inspected. The brushes are to be replaced at the 500 hour
   inspection, the starter-generator cleaned and an armature
   resistance check is to be carried out (to identify any path that
   may allow voltage to leak from the starter-generator). The
   allowable resistance values set by the operator are more
   restrictive than that recommended by the manufacturer of the
   starter-generator.

In addition, the aircraft manufacturer (Bombardier Aerospace,
Shorts Brothers plc) has issued the following service documentation
to aircraft operators:

1. SB360-24-24, dated December 2000, detailing the installation of
   a new earthing point between the engine firewall assembly and the
   starter-generator, to provide supplemental bonding for the
   starter-generator.
2. SIL SD360-IL-207, dated August 2000, detailing
   starter-generator removal and installation instructions and
   advising that operators ensure the integrity of the engine
   starter-generator electrical bonding.
3. SB360-72-01, dated December 2000, recommending that aircraft
   operators carry out Pratt & Whitney Canada Service Bulletin
   PT6A-72-13348 and PT6A- 72-14304 within 25 flight hours of a
   starter-generator failure or an unscheduled starter-generator
   removal during the last 1,000 flight hours.

The aircraft manufacturer has also advised that they have agreed
with proposed TRW Lucas modifications to electrically isolate the
starter-generator output shaft from the engine starter gear.

The engine manufacturer (Pratt and Whitney Canada) issued SB's
PT6A-72-14304, PT6A-72-13348 and PT6A-72-14318 on 15 Dec 2000
recommending engine oil filter patch inspections within 25 flight
hours. Those inspections may detect debris in the oil system,
originating from the number-one bearing area.

Safety Recommendations

As a result of this occurrence, the Australian Transport Safety
Bureau issues the following safety recommendations.

R20020120

The Australian Transport Safety Bureau recommends that the Civil
Aviation Safety Authority continue to examine the circumstances of
electrical discharge damage to the number-1 bearing of the Pratt
and Whitney (Canada) PT6A engine models equipped with TRW Lucas
starter-generators and develop an appropriate safety assurance
strategy to ensure the continuing airworthiness of Australian
registered aircraft fitted with similar engine and
starter-generator combinations.

R20020121

The Australian Transport Safety Bureau recommends that the
United States Federal Aviation Administration examine the
circumstances of electrical discharge damage to the number-1
bearing of the Pratt and Whitney (Canada) PT6A engine models
equipped with TRW Lucas starter-generators and develop an
appropriate safety assurance strategy.

SAN 20020122

The Australian Transport Safety Bureau suggests that Transport
Canada should note the deficiencies identified relating to
electrical discharge damage to the number-1 bearing of the Pratt
and Whitney (Canada) PT6A engine models equipped with TRW Lucas,
model 23078 and 23085, starter-generators.

SAN 20020123

The Australian Transport Safety Bureau suggests that Pratt and
Whitney Canada should note the deficiencies identified relating to
electrical discharge damage to the number-1 bearing of the Pratt
and Whitney (Canada) PT6A engine models equipped with TRW Lucas,
model 23078 and 23085, starter-generators.

SAN 20020124

The Australian Transport Safety Bureau suggests that the United
Kingdom Civil Aviation Authority should note the deficiencies
relating to electrical discharge damage to the number-1 bearing of
the Pratt and Whitney (Canada) PT6A engine models equipped with TRW
Lucas, model 23078 and 23085, starter-generators.

Technical Analysis
Report 200003399

1. The failure of the left engine was a result of the failure of
   the number-1 bearing.
2. The failure of the number-1 bearing in the left engine was a
   result of electrical arcing damage to the bearing inner race.
3. The number-1 bearing inner race electrical arcing damage was
   most likely a result of electrical discharge from the
   starter-generator assembly.

The most likely source of the electrical discharge damage was
the starter-generator unit, which couples directly to the
starter-generator gear. This was consistent with the failure
pattern in previous number-1 bearing failures in PT6A engines.
Tests carried out on a starter-generator of the same model as that
fitted to the failed engine, indicated that the problem is
exacerbated by the accumulation of brush dust. Armature leakage
electric current from the unit would be conducted via the dampener
assembly, through the starter-generator gear and to the number-1
bearing via the coupling gear and shaft assembly. Intermittent
pitting on the starter-generator gear and continuous pitting on the
coupling gear indicated that the most likely source of electric
potential was the starter-generator assembly. The effect of
utilising FAA PMA components rather than original manufacturer
parts in the overhaul of the starter-generators is
undetermined.

While in cruise flight between Bundaberg and Brisbane, the crew
of the Shorts 360 aircraft heard a loud noise followed by the
automatic feathering of the right propeller. The crew shut down the
right engine, declared a PAN and continued to Brisbane.