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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

CLASS XO.

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