C I V I L A V I A T I O N D E P A R T M E N T
A C C I D E N T I N V E S T I G A T I O N D I V I S I O N
Report on the accident
to
Beagle B121 Series II VR-HGZ
at
Lead Mine Pass, New Territories, Hong Kong
on
4th September 1978
April 1979
Civil Aviation DepartmentNew Rodney Block99 QueenswayHong Kong
April 1979
Your Excellency',
I have the honour to submit the report
by Mr. I. Hutchinson, an Inspector of Accidents, on the
circumstances of the accident to Beagle B121 VR-HGZ
which occurred at Lead Mine Pass, New Territories,
Hong Kong on the 4th September 1978*
I have the honour to be
Sir,
Your obedient servant
B.D* KeepChief Inspector of Accidents
His Excellency the Governor,Government House,Hong Kong.
— 1 —
Accident Investigation Division
Aircraft Accident Report No* 1/79
Operator
Aircraft Type
Model
Nationality
Registration
Place of Accident
Date of Accident
The Hong Kong Flying Club
Beagle
B121 Series II
British
VR-HGZ
Lead Mine Pass, Hong Kong
4th September 1978
SYNOPSIS
All times in this report are GMT
(Hong Kong Standard Time is 8 hours ahead of GMT)
The accident was notified to the Accident
Investigation Division of the Civil Aviation Department by
the duty Air Traffic Control Supervisor at Hong Kong
Airport. The investigation was carried out by an Inspector
of Accidents of the Civil Aviation Department.
The aircraft, with two persons on board, took off
from Hong Kong airport to proceed to a nearby military
aerodrome for landing practice. On the return flight, whilst
cruising at an altitude of 1500 feet, the engine suddenly lost
power and the aircraft started to descend. Attempts to
restore engine power were unsuccessful, and the aircraft
eventually crashed in hilly terrain at an elevation of 1250'
above mean sea level. One occupant suffered leg burns whilst
the other had minor facial injuries. The aircraft was
destroyed by impact and fire.
— 2 —
No reason for the loss of engine power has been
established,
1* FACTUAL INFORMATION
1,1. History of the Flight
VRHGZ was owned and operated by the Hong Kong
Flying Club for the use of club members. On the
morning of the 4th September 1978 the aircraft had
flown for one hour prior to the accident flight,
having been refuelled to maximum capacity of 36
imperial gallons on completion of the previous
days operations. Before the first flight of the
day a full pre-flight inspection was carried out,
including a fuel/water drain check. On the flight
in question the pilot had intended to fly solo but
happening to meet a friend at the club premises,
invited him to occupy the spare seat. The friend
in fact had flown some eleven hours as a student
pilot, but on this occasion his role was that of
a passenger. All pre-flight checks having proved
satisfactory, the aircraft departed Hong Kong
airport at 0301 hours GMT under Visual Flight Rules
and proceeded to a nearby military airfield at
Sek Kong for landing practice. The pilot occupied
the right hand seat with the passenger in the left
one, although under the rules of the club the
pilot should have been in the left seat.
The aircraft arrived over Sek Kong at 0316 and
carried out three Mtouch and go" landings on
Runway 29, during which some nosewheel shimmy was
noticed. However this was not unusual since the
aircraft had been prone to nosewheel shimmy for
some time. Following the third touch and go the
pilot decided to return to Hong Kong Airport.
- 3 -
The passenger subsequently stated that on climb-out
following this landing he thought he felt some
engine vibration, but the pilot did not notice
anything abnormal.
The aircraft left Sek Kong at approximately 0329
and carried out a normal climb to 1500 feet,
which is the standard outbound altitude when
departing the aerodrome traffic zone. At approxi-
mately 0332 having levelled-off the pilot selected
a low cruise power setting of 2100 r.p.iru, and
continued the flight at 1500 feet on an easterly
heading for a few seconds before turning to the
right to achieve a more direct routing to Hong Kong
airport. This route takes aircraft through a gap
in the hills known as Lead Mine Pass. The pass is
a valley with mountains on either side, the floor
of the valley rising towards the south to a
maximum height of 1300 feet above mean sea level
before falling sharply away again towards a
reservoir. According to the pilot he would
normally have initiated a climb shortly after
entering the valley, but on this occasion before
he had attempted to do so he sensed the aircraft
was descending and noticed that the engine speed
indicator was showing about 1400-1500 r.p.nu
He advanced the throttle, but this had no effect.
He stated that the engine was not running roughly
nor was it indicating signs of obvious malfunction
such as banging or spluttering. He then switched
on the fuel booster pump, checked that the fuel
contents were adequate (there were approximately
14 gallons in each tank), checked the fuel
selector which was selected to feed fuel from
both tanks, that the mixture control was on "rich11,
and that both magnetos were selected on. Moving
the throttle again did not produce any response,
- 4 -
and the pilot was therefore unable to restore power
to the engine. By this time the aircraft was
nearing the ground and the pilot was faced with
a crash landing. He considered trying to turn
back towards lower ground but decided his height
was insufficient and all he could do was to try
and stretch the glide over the top of the pass
and down the other side towards the reservoir,
meanwhile hoping that the engine would regain
power* An added complication was the presence of
electricity high-tension cables with supporting
30 feet high steel lattice towers immediately to
the right of the aircraft which he had to avoid.
Flying speed was soon lost and the aircraft stalled
onto the ground at a height of 1250 feet a.m.s.l.
in rough scrub-covered terrain liberally sprinkled
with large boulders. It caught fire immediately
and was destroyed. The occupants managed to
escape, although with varying degrees of injury.
A witness, who reported the accident to the police
authorities, was some 1% miles north of the
accident site. He saw the aircraft appear about
1 mile to his west from the direction of Sek Kong
and turn right towards Lead Mine Pass. He could
not hear it and did not see anything unusual.
On turning right the aircraft started to lose
height rapidly and, about twenty seconds later,
crashed into the hillside. It appeared to him to
be trying to climb again just before the crash.
The accident occurred in daylight, at approximately
0335 hours in position 22°25'N 114°09'E, at an
elevation of 1250 feet above mean sea level.
5 -
1.2. Injuries to persons
Injuries Crew
Fatal
Serious -
Minor/None 1
1.3. Damage to aircraft
The aircraft was destroyed.
1*4. Other damage
None.
1.5. Personnel Information
1.5.1. Pilot-in-command
Age:
Licence:
Limitations:
Aircraft Ratings:
Certificate ofExperience:
Medical Certificate:
Total flying hours:
Total hours on type;
Passengers
1
Others
49
Private Pilots Licence
None
Aircraft Group 'A1
Night Rating
Issued 23rd August 1978,valid until 22ndSeptember 1979.
Last medical 20th March1978, valid to31st March 1979.
392
37
Aircraft Information
1,6.1. Description of aircraft
VRHGZ was a Beagle B121 Series II aircraft.
This is a single engined low wing monoplane
powered by a Lycoming 0-320 A2B four
cylinder engine driving a two bladed fixed
pitch propellor, and having a fixed under-
carriage. GZ was fitted with dual controls
with one full set of blind flying instruments
positioned on the left side of the instrument
panel. The engine instruments were grouped
on the centre panel with the engine
switches below them. The throttle and
- 6 -
mixture control levers were on the centre console,
with a second throttle lever by the left cockpit
wall. The fuel tank selector control was located
on the floor of the cockpit in front of the left
hand seat.
1.6.2. Details of aircraft
Constructors Serial Number:
Certificate of Airworthiness;
Maintenance:
Total airframe hours:
Total airframe hours sinceC of A renewal:
Engine serial number;
Hours since manufacture:
Hours since last overhaul:
Maximum total weightauthorised:
Accident weight:
Centre of Gravity limits:(at accident weight)
Centre of Gravity at timeof accident:
Fuel on board at time ofaccident:
Type of fuel:
B121/083
In the Private
Category and valid
until 13th April 1979.
The aircraft had been
maintained in
accordance with the
appropriate main-
tenance schedule.
5125
259
RL~17Q63~274
Not known
1263
873 kg.
847 kg. (estimated)
between 66.5 and
71.3 inches aft of
datum
67.7 inches aft of
datum (estimated)
27 imperial gallons
(estimated)
AVGAS 100/130
— 7 —
1.6.3. Other aircraft information
Three Service Bulletins have been issued relating
to throttle controls on the Beagle B121 Series II*
Two of these were in 1973; the first in April
which referred to the carburettor throttle arm
lever (retighten and fit locking wire), and the
second in September which introduced a carburettor
serrated throttle lever and shaft assembly. Both
these bulletins had been complied with on the
accident aircraft. On the 9th May 1977 this
aircraft experienced a fracture of the throttle
cable rod during engine start. On the 25th
October 1977 a Mandatory Service Bulletin No.
B121/74 - Failure of Throttle Cable Assembly -
introduced a modified throttle cable assembly,
(Mandatory Modification BE 424). This modified
cable assembly was fitted to GZ on the 10th
April 1978.
1.7. Meteorological Information
The 0330 weather observation at Hong Kong airport, which
is 6% nautical miles SSE of the accident site was :-
Surface wind: 120/5 knots
Cloud: 3/8 at 1,800 feet
5/8 at 14,000 feet
Visibility: 10 kilometres
Temperature: 31 C
Dewpoint: 25°c
An unofficial observation by the pilot of a rescue
helicopter over the accident area estimated the cloud as
4/8 cumulus at 3,000 feet, with a visibility of at least
10 kilometres.
Weather is not considered to be a factor in the accident.
- 8 -
1.8. Aids to navigation
Not applicable.
1.9. Communications
VHF/RT communications with Hong Kong Tower on 118.7 MHz,
and with Sek Kong on 121.1 and 122.4, were normal. The
time injection signal on the Sek Kong R/T recording
system was not functioning correctly, but it is estimated
that the last transmission from GZ was made at 1132.
This was a position report and placed the aircraft
approximately 2̂ nautical miles NW of the accident site.
1.10. Aerodrome information
Not applicable.
1.11. Flight recorders
There was no requirement for flight recorders and none
were fitted.
1.12. Wreckage and impact information
1.12.1. Accident site
The aircraft had contacted the ground at a low
forward speed, and in a landing attitude, almost
directly beneath the electricity cables
previously mentioned. The impact site has a
surface gradient of 1 in 8, and also slopes
transversely. The gradient of the surrounding
area averages around 1 in 5 in the direction of
flight. Due to the nature of the terrain it has
not been possible to determine with any accuracy
the angle of impact, but the evidence indicates
that within a few feet of first striking the
ground the aircraft was abruptly stopped when the
under-carriage and port wing struck large boulders
which abound in the area. The impact turned the
aircraft to port and the fuselage came to rest on
a heading of 155° magnetic, the heading prior to
impact having been about 183°. The raainspar
- 9 -
was moved a further 30°, approximately, to the left
and was also twisted downwards on the right hand
side as the starboard under-carriage was bent
backwards. The resultant pitch forward caused
the lower engine cowling and the propellor to
come into contact with other boulders inflicting
substantial damage.
There was no scattering of wreckage, all parts
being contained within an area roughly
corresponding to the normal dimensions of the
aircraft* An intense fire which broke out
immediately on impact consumed the whole of the
fuselage from the engine bulkhead to the tailplane,
and caused considerable additional damage to the
tailplane, fin and rudder, and both wings*
The engine itself was substantially intact
although many components of the fuel and
ignition systems, as well as the engine controls,
were destroyed by fire* The cockpit ignition
switch was recovered, and proved to be jammed in
the "BOTH" position.
1.12.2* Examination of wreckage
The engine and propellor were subjected to detailed
examination* This did not reveal any mechanical
failure that could have caused the sudden loss of
power* The carburettor was completely detached
from its mounting aperture and resting on top of
the exhaust manifold* The rear portion of the
carburettor mounting flange was broken and
remained attached to the oil sump case, and the
front mounting studs on the sump case were sheared.
The throttle cable was broken at the carburettor
end* Due to severe external overheating the fuel
pump, carburettor, magnetos, and high tension leads,
- 10 -
could not be functionally tested but the
examination did not indicate any mechanical
failure of these parts* The condition of all
sparking plugs was normal.
The fractured carburettor mounting aperture,
carburettor front mounting studs, and throttle
cablef were further subjected to metallurgical
examination* However, in no case was there
sufficient evidence to suggest that any
pre-impact damage or defect existed.
The condition of the engine, propellorf and the
engine/propellor attachment fittings suggests
that at the time of impact the propellor was
rotating under low power.
1«13. Medical and pathological information
The 'pilot suffered superficial burns to the face, other
minor injuries to the face, and bruising of the right
knee. The passenger was burned on both legs which
resulted in his being hospitalised for 20 days followed
by further treatment as an out-patient.
1.14. Fire
Very severe fire broke out immediately on impact which
consumed the cockpit and a large part of the fuselage.
It also caused considerable post-impact damage to the
wings and the tailplane assembly.
1.15. Survival aspects
Both the pilot's and the passenger's seats were equipped
with a full safety harness.
Both occupants were able to escape from the aircraft
almost immediately, although one had momentary difficulty
through failure to release his harness before trying to
leave, and were subsequently picked up by a military
helicopter.
- 11 -1.16. Tests and research
Although no identical aeroplane was available in Hong Kong9tests were carried out on a related type having similar
performance characteristics* These indicated that :
(1) In the circumstances as described by the pilot and
passenger any attempt to turn back towards the lower
ground or water to the north would have ended in
disaster, due to the narrowness of the valley and
the steepness of the hills on either side.
(2) The time interval between losing engine power and
impacting the ground would have been of the order of
20 seconds. This time coincides with that estimated
by the passenger and by the eyewitness.
1.17. Additional information
1.17.1.- Geographical information
A military aerodrome traffic zone is establised
at Sek Kong aerodrome to an altitude of 2,500 feet.
Outside the traffic zone the airspace is
uncontrolled up to 3,500 feet. Around the
boundary of the zone four entry and exit check
points are located. Entry and exit to or from
Sek Kong must be by one of the four routes served
by these check points, and must be made at the
standard altitudes of 1,500 feet for departing,
and 2,000 feet or above for arriving, traffic.
An aircraft flying from Sek Kong to Hong Kong
airport would normally exit via a check point
situated just over two nautical miles east of
the runway.
On a direct track from Sek Kong to Hong Kong
airport the ground rises to over 3,000 feet, so
it is usual to make a detour in order to avoid the
highest peaks. There are two possible ways to do
this, one being via Lead Mine Pass which has a
maximum elevation of 1,300 feet. The other is
- 12 -
to take a slightly longer route over lower ground
and coastline to a position approximately three
and a half miles north of the airport. It is
in either case then necessary to cross a line of
hills with a high point of 1,600 feet in order to
reach the traffic circuit.
1.17.2* Emergency drills
The Beagle flight manual lists the following
actions to be carried out when faced with a forced
landing:~
1. Immediate actions:
Close throttle, gaining height if possible
while reducing speed to 70 knots for the glide.
Select suitable landing area noting wind
strength and direction.
Check altimeter setting.
Plan descent.
2. Subsequent actions:
Check for cause of failure (fuel selection,
ignition switches, icing, mixture).
Make R/T distress call.
3. Crash landing checks:
Fuel mixture - Select to cut off
Fuel booster pump - Off
Ignition switches - Off
Fuel tank selector - Off
Harness - Secure and tight
Brakes - Off
4. Before landing switch off the battery master
switch.
- 13 -
1.17.3. The engine manufacturer was consulted regarding
the likely effect on engine speed of a
breakage between the throttle control and the
carburettor. His opinion was that the spring
on the throttle plate shaft would be counter-
acted by the accelerator pump and therefore
the power setting would be likely to remain
in the original position.
1*18. New investigation techniques
None.
2* ANALYSIS
2.1. General
The evidence of the pilot and passenger indicates
that whilst cruising in level flight at 1500 feet
the aircraft's engine lost virtually all power, and
the actions subsequently taken by the pilot to
restore normal operation were unavailing. The
aircraft was at this time flying over hilly terrain,
the nature of which made it extremely unlikely that
a successful forced landing could be carried out.
In the ensuing crash a large portion of the
aircraft, including the cockpit and most of the
fuselage, was completely destroyed by fire* Although
the engine itself was virtually intact, the bottom
portion of the cowling was badly damaged and the
various components of the fuel and ignition systems
either destroyed or so badly damaged by impact or fire
that functional testing was not possible. However,
strip examination of the engine and available system
components has not revealed any mechanical failure
that would explain the sudden loss of power*
- 14 -
The pilot occupied the right hand seat with the
passenger in the left. This arrangement is not usual
since there is only one set of flight instruments,
located in front of the left hand seat. Furthermore,
sitting in the right seat the pilot would have
experienced some difficulty in operating the fuel
tank selector switch, but this is not considered
to be a factor in the accident since there would have
been ample fuel remaining in both tanks.
Although local flying rules limit aircraft on
departure from Sek Kong to 1500 feet until clear of
the entry and exit check points, in view of the nature
of the terrain between Sek Kong and Hong Kong airport
it may well be thought prudent when intending to
follow the Lead Mine Pass route to climb higher as
soon as the check point has been passed, or alter-
natively to take the slightly longer route over less
inhospitable country..
2.2. Engineering aspects
Since examination of the engine and those associated
components which were recovered has not revealed any
failure which could be responsible for the loss of
power it is necessary to examine the most likely
possibilities in greater detail.
Certain causes of engine failure can be considered as
unlikely since they would normally be accompanied by
obvious signs of malfunction such as very rough
running, spluttering, or banging. In this case,
according to the pilot, there were no such symptoms.
The following possible explanations will be discussed
here: carburettor intake icing, fuel contamination,
fuel starvation, ignition system failure, and
failure of the throttle control system.
- 15 -
(a) Carburettor intake icing
Carburettor icing would commonly, but not
invariably, be accompanied by rough running and
exhaust smoke. The single eyewitness did notnotice any smoke, but he was a considerable
distance away. Also the rapid decay of engine
revolutions is not typical of carburettor
icing. The sparking plugs were found onexamination to be relatively dry, and the
electrodes were of a normal operating colour.Following exposure to icing conditions spark
plugs would usually show signs of dampness and
carbon deposits, due to enrichment of thefuel/air mixture.
Carburettor icing is more likely to occurfollowing prolonged engine running at a low
power setting; it is not normally associated
with the flight pattern of GZ which involveduse of take-off and climbing power until three
minutes before the failure. Finally, therelatively high ambient temperature would also
render this type of hazard unlikely.
For these reasons it is considered that
carburettor intake icing can be discounted.
(b) Fuel contaminationGZ had been refuelled to maximum capacity the
evening before the accident. Prior to the first
flight on the day of the accident a normalpre~flight inspection was carried out, and this
included a fuel/water drain check. Subsequently
the aircraft had flown for one and a halfhours before the power loss occurred, duringwhich time it could be expected to consume
about one quarter of the total capacity.
- 16 -
Several other piston-engined aircraft are
refuelled from the same source as GZ; in no
case has there been any suggestion of fuel
problems.
The use of fuel contaminated by water or other
alien matter could be expected to produce rough
or uneven running, as well as loss of power.
It is considered that contamination of the fuel
can therefore be ruled out.
(c) Fuel starvation
The aircraft was refuelled to maximum capacity
of 36 gallons the evening prior to the accident
and had flown one and a half hours subsequently.
The pilot thought that when he checked the fuel
contents immediately the engine started to give
trouble there was about fourteen gallons in each
wing. The nature of the fire damage following
impact also testifies to the presence of fuel
in the aircraft.
The possibility of complete fuel exhaustion can
therefore be dismissed. Fuel starvation to the
engine could be caused in several ways such as
by blocked or partially blocked fuel filters or
fuel lines, leakage of fuel lines, sticking
carburettor jet or float, or other malfunction
of the carburettor. Other possible causes would
be failure of the fuel pump(s), or throttle or
mixture controls. Functional testing of the
carburettor was not possible due to heat damage.
If the fuel supply was blocked completely the
engine would stop, or merely windmill, and this
did not happen. Since they are mechanically
linked, any movement of the throttle lever would
result in a corresponding movement of the
accelerator pump. Therefore, if the fuel supply
- 17 -
was only partially blocked a forward movement of
the throttle would tend to cause a temporary
increase in engine speed, whereas the pilot
states that no such increase occurred. The same
considerations apply to a malfunction of the
mixture control system, forward movement of the
throttle could be expected to have a temporary
effect on engine speed*
Although the mechanical fuel pump was examined, a
functional check was not possible. Failure of
the mechanical engine driven pump, with the
electric booster pump switched off, will cause the
engine to stop. The pilot states that the booster
pump was selected on following the loss of power.
However the time interval cannot be stated with
accuracy, and if the mechanical pump had
partially or completely failed it may be that
insufficient time remained for adequate fuel
pressure to be regained.
It is considered that failure of the mechanical
fuel pump as a factor in the accident is unlikely,
but nevertheless cannot be excluded completely,
(d) Failure of the ignition system
Failure of one of the two magnetos would result
in a drop in engine revolutions of not more than
100-150 r.p.m., probably accompanied by some
roughness* Functional testing of the magnetos
and high tension leads to the spark plugs was not
possible due to heat damage. The plugs themselves
were relatively dry and of a normal colour, whilst
bench tests confirmed that they would still
function satisfactorily. Since a sustained drop in
engine speed of about 700 r.p.iru without rough
running was reported, ignition problems seem
unlikely.
- 18 -
(e) Failure of the throttle control system
The fact that three service bulletins have been
issued relating to throttle controls on the Beagle
B121, and also that this particular aircraft had
on a previous occasion experienced a fracture of
the throttle cable during engine start-up, points
to the possibility that a similar failure could be
the principal cause of the accident.
There is no return spring in the throttle control
system, there is however, a spring on the throttle
plate shaft of the carburettor. The engine
manufacturer is of the opinion that this spring
would be counteracted by the accelerator pump,
and therefore the throttle would tend to remain
as set in the event of a breakage between the
throttle control and the carburettor. Nevertheless
the throttle plate could move, perhaps under the
influence of vibration or airflow through the
intake. Consequently it would be possible for the
engine speed to decay to a lower setting and,
subject to variations with any change in airspeed
since the propellor had a fixed pitch, to remain
at that setting. On the other hand, at the time
the loss of power occurred the throttle lever
was not being moved and it seems doubtful if the
system would break in this way without some sort
of movement to initiate the failure.
A failure of the throttle control system could
however ac<itount for the loss of power, and would
be consistent with the symptoms as described by
the pilot, even though detailed examination of
the wreckage has revealed no evidence to sub-
stantiate such a hypothesis.
- 19 -
2.3. Action in emergency
The forced landing emergency drills as listed in
the flight manual are partly, although not completely,
applicable to this accident. The statement by the
pilot indicates that he took all the steps which were
open to him in an attempt to restore engine
performance. He had little, if any, choice over
selection of the touchdown area. No R/T distress
call was made, due to the very limited time available.
The crash landing checks, which are mainly concerned
with closing down the fuel system and switching off
electrical power, were not carried out since the
pilot continued until the moment of impact to hope
that power would be restored. How much this affected
the speed and severity of the subsequent fire can
only be a matter for conjecture; however, it seems
reasonable to assume that the fractured carburettor
mounting adjacent to the exhaust manifold together with
its associated broken fuel lines may well indicate
the source of the outbreak.
3. CONCLUSIONS
(a) Findings
(i) The aircraft had been maintained in accordance
with an approved maintenance schedule and its
documentation was in order.
(ii) The weight and centre of gravity were within
the prescribed limits.
(iii) The pilot was properly licenced for the flight,
(iv) The fuel carried on the aircraft was ample
for the proposed flight,
(v) Whilst flying over rough, hilly terrain enroute
from Sek Kong military aerodrome to Hong Kong
airport, the engine suddenly lost power.
- 20 -
(vi) The ground in the area was covered in scrub
and large scattered boulders and this factor,
together with the surface gradient, made a
forced landing extremely hazardous. Howeverf
the aircraft was not high enough to reach
a more suitable area.
(vii) The pilot was unable to restore engine
performance and, in the enforced attempt to
land, the aircraft collided with large boulders
and was destroyed.
(viii) The reason for the loss of engine power has not
been determined.
(b) Cause
The accident resulted from a loss of engine power
whilst the aircraft was flying over hilly ground which
was unsuitable for a forced landing. No reason for
the loss of power has been determined.
I. HutchinsonInspector of Accidents
Accident Investigation DivisionCivil Aviation DepartmentApril 1979
[HKP] 629.13255 H7 B78
"̂ UK P^629.13255
—1284640
Hong long. Civil Aviation Depart-ment* Accident InvestigationDivision,
on T 1
Date Due 1284640
NOTOC