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CA 12-12a 23 FEBRUARY 2006 Page 1 of 18

Section/division Accident & Incident Investigations Form Number: CA 12-12a

AIRCRAFT ACCIDENT REPORT AND EXECUTIVE SUMMARY

Ref No CA18/2/3/9396

Aircraft Registration ZS-RAX Date of Accident 17 January 2015 Time of Accident 1305Z

Type of Aircraft Robinson R44 Raven II (Helicopter) Type of Operation Private

Pilot-in-command Licence Type Private Age 47 Licence Valid Yes

Pilot-in-command Flying Experience Total Flying Hours 490.3 Hours on Type 397.6

Last point of departure George aerodrome (FAGG), Western Cape province

Next point of intended landing George aerodrome (FAGG), Western Cape province

Location of the accident site with reference to easily defined geographical points (GPS readings if possible)

Cradock peak at GPS position determined as South 33°53 ´, 68″ and East 022°27 ´, 59″ at an elevation of approximately 5 177 ft AMSL.

Meteorological Information Temperate, 20°C: Wind direction, south east: Clear skies: Visibility, 10

km: Wind speed, light: Pressure altitude, 4 890 feet AMSL.

Number of people on board 1 + 2 No. of people injured 0 No. of people killed 0

Synopsis

The pilot accompanied by two passengers took off from George (FAGG) aerodrome on a

private flight bound for Cradock peak. According to the pilot, the intention of the flight was to

observe the landscape from the mountain peak and then return to FAGG. Take-off clearance

was granted and the helicopter lifted off and hover taxied. The helicopter then climbed to

6 000 feet above mean sea level (AMSL) and routed in a northerly direction at 70 knots

indicated air speed (AIS). On final approach for landing on the mountain peak, the low rotor

revolution per minute (RPM)/blade stall warning light came on, followed by the annunciator

horn. The pilot instantly lowered the collective lever in an attempt to recover the RPM to the

green arc, but without success. The helicopter drifted and landed hard on a rocky slope

damaging the skids/lower fuselage area. The helicopter severed the top of the tail boom

during the process. The helicopter remained upright and the pilot and the passengers

disembarked uninjured. The investigation concluded that the accident was caused by

downdraft conditions in the area at the time the pilot was initiating a landing.

Probable Cause

Poor technique.

IARC Date Release Date


Section/division Accident & Incident Investigations Form Number: CA 12-12a

AIRCRAFT ACCIDENT REPORT

Name of Owner/Operator : LCT Communications CC

Manufacturer : Robinson Helicopter Company

Model : R44 Raven II

Nationality : South African

Registration Marks : ZS-RAX

Place : Cradock peak

Date : 17 January 2015

Time : 1305Z

All times given in this report are Co-ordinated Universal Time (UTC) and will be denoted by (Z). South

African Standard Time is UTC plus 2 hours.

Purpose of the Investigation:

In terms of Regulation 12.03.1 of the Civil Aviation Regulations (1997) this report was compiled in the

interest of the promotion of aviation safety and the reduction of the risk of aviation accidents or incidents and

not to establish legal liability.

Disclaimer:

This report is given without prejudice to the rights of the CAA, which are reserved.

1. FACTUAL INFORMATION: 1.1 History of Flight:

1.1.1 On Saturday 17 January 2015, the pilot accompanied by two passengers took off

from George (FAGG) aerodrome on a private flight bound for Cradock peak, about

5 177 ft above mean sea level (AMSL) and located in the Eden district municipality.

Visual meteorological conditions prevailed and no flight plan was filed. According to

the pilot, the intention of the flight was to observe the landscape from the mountain

peak and then return to FAGG. Before departure the pilot completed a detailed pre-

flight inspection and the aircraft had 48 US Gallons of Avgas LL100 fuel on board.

Nothing abnormal was observed and the passengers boarded the aircraft. The pilot

made sure that all passengers were properly harnessed and later provided a safety

briefing as well.


1.1.2 The pilot then boarded the helicopter and completed the before start checklist

before starting the engine. Take-off clearance by FAGG tower controller was

granted and the helicopter lifted off and hover taxied. The helicopter then climbed

to 6 000 feet AMSL and flew in a northerly direction at 70 knots. According to the

pilot, visibility was good and the flight took about 18 minutes. Before landing on the

peak, the pilot circled the helicopter three times and scanned the area for a suitable

landing spot and the wind direction. The pilot performed a power check and all was

fine. On final approach south-easterly into wind at 30 knots, the helicopter hovered

and descended. Moments afterwards, the low rotor revolution per minute

(RPM)/blade stall warning light came on, followed by the annunciator horn. The

helicopter began an uncontrolled descent and the pilot instantly lowered the

collective in an attempt to recover the RPM to the green arc, but without success.

The rotor tachometer dropped and the helicopter drifted followed by a hard landing

on a rocky slope damaging the skids/lower fuselage. Figure 1 shows the Robinson

R44 instruments panel.

Figure 1: The helicopter’s low rotor RPM/blade stall warning light and the tachometer

1.1.3 During the process, the main rotor struck the tail boom. The helicopter remained

upright and the pilot switched off the master and alerted FAGG tower controller at

frequency 128.20 Megahertz. The pilot and the passengers disembarked uninjured.

Another helicopter was dispatched to rescue the occupants, which later landed at

FAGG without incident. The post pilot interview revealed that he had landed this

helicopter at this site numerous times in the past, but had not completed mountain

flying course. The flight was conducted under the provisions of Part 127 of the Civil

Aviation Regulations of 1997, as amended and the operator was in possession of a

valid air operating certificate.

The low rotor RPM warning light and tachometer


1.1.4 The accident occurred approximately 7.9 NM, northerly of FAGG at GPS co-

ordinates determined as South 33°53 ´, 68″ and East 022°27 ´, 59″ at an elevation of

approximately 5 177 ft AMSL. Figure 2 is the Google Earth map depicting the

accident site.

Figure 2: Google Earth map depicting Cradock peak

1.2 Injuries to Persons:

Injuries Pilot Crew Pass. Other

Fatal - - - -

Serious - - - -

Minor - - - -

None 1 - 2 -

1.3 Damage to Aircraft:

1.3.1 Damage was limited to the tail boom and the skids/lower fuselage. Attached below

are the pictures.


Figure 3: Final position of the helicopter on a rocky slope

Figure 4: Damaged tail boom

1.4 Other Damage:

1.4.1 None.

Damaged left hand skid and dents sustained on the lower fuselage section


1.5 Personnel Information:

Nationality South African Gender Male Age 47

Licence Number 0270499460 Licence Type Private

Licence valid Yes Type Endorsed Yes

Ratings Night Rating

Medical Expiry Date 30 September 2015

Restrictions Nil

Previous Accidents

Incident report CA18/3/2/0523 dated 02 October 2005

indicated that the ZS-RAX helicopter had in-flight blade

vibrations as a result of a cracked/delaminated main rotor

blade serial No 2981C.

Flying Experience:

Total Hours 490.3

Total Past 90 Days 36.8

Total on Type Past 90 Days 36.8

Total on Type 397.6

1.6 Aircraft Information:

1.6.1 Helicopter description:

The Robinson R44 Raven II is a single-engine four-seater light utility helicopter

constructed primarily of metal and equipped with skid-type landing gear. The

helicopter is powered by an IO540 six-cylinder horizontally opposed fuel-injected

engine with angled valve head and tuned induction capable of producing 300

horsepower. The engine is controlled by an electronic governor, also manufactured

by Robinson. Fuel is fed by gravity, with an electric prime pump. Should the engine

inadvertently shut down, the loss of oil pressure turns the pump off, preventing the

engine from flooding during a restart. The output shaft powers both the cooling fan

and the drive belt sheave.


The cooling fan provides air to cylinder heads and oil coolers, and also serves for

gearbox cooling and cabin heating. The main rotor system is a two-blade under

slung teetering hinge. The all-metal stainless steel blades are connected to the hub

by two sealed Teflon-coated coning hinges. The pitch change bearings are wet and

enclosed by a neoprene boot at the blade root. The main gearbox contains a single-

stage splash-lubricated gear set and is driven by a V-belt sheave that lies directly

above the engine sheave. The sprag one-way drive clutch is contained within the

upper sheave and can easily be checked for operation by the pilot on pre-flight. An

automatic clutch actuator raises the upper sheave when the pilot engages the

clutch, and a tensioner automatically stops the engagement when the correct

tension is achieved.

It also automatically adjusts tension in flight. The tail rotor drive does not have any

hanger bearings; it drives a splash-lubricated gearbox. The two metal tail rotor

blades are attached to a teetering hub with a fixed coning angle, and use

elastomeric teetering bearings and Teflon pitch-change bearings. The hydraulic

system consist of a pump, three servos, a reservoir and lines boosting the main

rotor flight control while eliminating cyclic and collective feedback forces. At the

same time the flight controls maintain a direct mechanical link, allowing full control

should the hydraulics fail. The pump is driven by the main gearbox, operating at a

relatively low pressure of 450 to 500 PSI. The pilot can turn the hydraulics off,

although electrical power is required to do so, providing a fail-safe system. The 28-

volt DC electrical system powers a single bus bar and includes an alternator,

voltage controller and 24-volt battery.

Standard lighting on the R44 helicopter includes strobe, navigation, panel and map

lights. The warning lights are extensive, and the low rotor warning also includes a

horn activated at 97 per cent rpm. Another standard feature is the four-place voice

activated intercom system. The helicopter has a press-to-talk (PTT) switch in the

pistol grip on the cyclic control, which is activated by the index or key finger. The

hydraulic switch is located on the front of the cyclic stick. All the equipment has

been installed for easy accessibility for the observer or pilot in day or night

operations, including independent audio controls, map lights and a pouch for

binoculars. Removable left seat pedals and collective control may be installed to

allow a rated co-pilot to control the helicopter using the centre cyclic control. Below

is the helicopter’s drive system. Figure 5 below shows the helicopter’s drive system.


Airframe:

Type Robinson R44 Raven II

Serial Number 11373

Manufacturer Robinson Helicopter Company

Year of Manufacture 2006

Maximum Operating Altitude 14 000 ft

Hover Ceiling IGE 8 950 ft

Hover Ceiling OGE 7 500 ft

Maximum take-off weight 2 500 lb

Empty weight 1 523.5 lb

Total Airframe Hours (At time of Accident) 962.3

Last MPI (Hours & Date) 936.2 20 November 2014

Hours since Last MPI 26.1

C of A (Issue Date) 05 September 2006

C of A (Expiry Date) 04 September 2015

Airworthiness Directives and Service

Bulletins Complied with

C of R (Issue Date) (Present owner) 06 July 2011

Fuel used Avgas LL 100

Operating Categories Standard Part 127

Figure 5: A picture depicting the R44 drive system


*NOTE: The operating categories for the helicopter were specified as commercial,

allowing use for transport by the operator, LCT Communications CC. The last

mandatory periodic inspection carried out on the helicopter prior to the accident was

certified at 936.2 hours on 20 November 2014 by an approved aircraft maintenance

organisation (AMO) No 1263.

1.6.2 Engine:

Type Lycoming IO-540-AE1A5

Serial Number L-31413 48A

Hours since New 962.3

Hours since Overhaul T.B.O not yet reached

1.6.2 ZS-RAX Weight and balance calculation at departure:

Weight

(lbs)

Arm

(inches)

Moment

(in.lb)

A/C empty weight 1 460 107.4 15 6804

Right front pilot (90kg) 198 49.5 9 801

Left front passenger (80kg) 176 49.5 8 712

Left aft passenger (80kg) 176 79.5 13 992

Baggage (08kg) 17.6 79.5 13 99.2

Fuel main tank (30 US gall) 180 106.0 1 9080

Fuel aux tank (18 US gall) 108 102.0 11 016

Total T/O Weight 2 315.6 95.35 220 804.2

The Maximum Certificated take-off Mass for the helicopter as stipulated in Section

2, page 2 to 3 of the POH (Pilot’s Operating Handbook) is given as 2 500 pounds

(1134 kg). Centre of Gravity (CG) = Total Moment ÷ Weight

= 220 804.2 ÷ 2 315.6

= 95.35 inches


(i) The fuel conversion factor used to compile this report was: 1 US Gallon = 6

pounds.

(ii) It is indicating that the helicopter was operated within its allowable envelope

as indicated on the following graphs.


(vi) The in ground effect (IGE) hover graph, as documented in the POH, Section

5, page 5-3 was studied. The graph indicated that the IGE hover at 4 890

feet pressure altitude at 20°C and a gross weight o f 2 315.6 lbs would have

been possible.

(vii) The helicopter performance in relation to the out of ground effect (OGE)

hover graph, indicated that the maximum out of ground hover gross weight at

4 890 feet pressure altitude and 20°C should not ex ceed 2 414 lbs. The

maximum gross weight for the helicopter on take-off was 2 315.6 lbs,

meaning that it was within the OGE calculated limit by 98.4 lbs.


1.7 Meteorological Information:

1.7.1 Weather information as obtained from the pilot’s questionnaire:

Wind direction South east Wind speed Light Visibility 10 km

Temperature 20°C Cloud cover Nil Cloud base Nil

Dew point N/a

4 890 ft

2 315.6 lb


1.7.2 Density altitude

Pressure altitude 4 890 ft

Temperature 20°C

Density Altitude 6 567 feet

1.8 Aids to Navigation:

1.8.1 The helicopter was equipped with standard navigational equipment as per the

minimum equipment list approved by the regulator.

20°C

6 567 ft


1.9 Communications:

1.9.1 The helicopter was equipped with standard communication equipment as per the

minimum equipment list approved by the regulator

1.10 Aerodrome Information:

1.10.1 The accident occurred at Cradock peak and not at the aerodrome.

Figure 6: Area map depicting FAGG and the accident site


1.11 Flight Recorders:

1.11.1 The helicopter was not fitted with a Cockpit Voice Recorder (CVR) or a Flight Data

Recorder (FDR) and neither was it required to be fitted to this type of helicopter.

1.12 Wreckage and Impact Information:

1.12.1 The helicopter approached south easterly and landed hard on a rocky slope

severing the tail boom and the skids/ lower fuselage area. Control continuity was

confirmed for all flight controls in the helicopter; none of the components showed

signs of disconnection or failure. The continuity of the tail rotor drive train and the

tail rotor pitch control linkage was established. The main and tail rotor gearboxes,

as well as the engine freewheel unit, were examined and no malfunction or pre-

existing anomaly was found. The damage to the main rotor blades is consistent with

a rotor system striking the tail boom while turning at moderate RPM, and is a sign of

moderate rotor energy. All the seats structures remained intact. Figure 7 and 8

shows the position of the helicopter on the crash site.

Figure 7: Final position of the helicopter at the accident site


Figure 8: Rear view of the helicopter and the terrain

1.13 Medical and Pathological Information:

1.13.1 Not applicable.

1.14 Fire:

1.14.1 There was no evidence of a pre or post impact fire.

1.15 Survival Aspects:

1.15.1 The helicopter remained intact and the occupants were properly restrained prior to

take-off by making use of the helicopter equipped three point safety harness. None

of the safety harnesses had failed.

1.16 Tests and Research:

1.16.1 None considered necessary.


1.17 Organizational and Management Information:

1.17.1 This was a private flight.

1.17.2 The last MPI (Mandatory Periodic Inspection), prior to the accident was certified by

AMO (Aircraft Maintenance Organisation) No 1263. The AMO was in possession of

a valid AMO approval certificate.

1.18 Additional Information:

1.18.1 Principles of helicopter flight, by W.J. Wagtendonk, Chapter 23.

The hazards of mountain flying are as follows:

• Updrafts and downdrafts that jeopardize control of the helicopter.

• Rapid changes to total thrust during the landing phase that may contribute to a hard touchdown or force the helicopter back onto the ground on lift-off.

• Rapid and unpredictable changes to translational lift values.

• The possibility of retreating blade stall in vertical gust or updrafts.

• Risk of mast bumping in severe updraft (negative g) situations.

The “Standard” Mountain Approach:

The word “standard” is emphasized because there is no standard approach that

always holds well in mountainous terrain operations. Standard is used to identify

basic mountain approach considerations that influence the selection of an

appropriate approach profile. The standard approach, consist of an approach

directly into the wind using the constant angle landing technique. The landing is

normally preceded by a hover, but zero-speed or run-on-landings are alternatives.

Landings on mountain ridges into the wind may place the aircraft on a lee side of

the ridge during the approach, in which case the steepness of the approach angle

should be adjusted as on figure 9 below.


Figure 9: Approach angle variations with different wind speeds

If the wind or turbulence prevents the standard approach, the approach can be

made along the ridge, angled or from the upwind side. In all cases a

reconnaissance should be flown along the ridge at a slow but safe speed establish

the best final approach direction and to check for obstacles. A helicopter

approaching from the windward side risks drifting into the downdraft area after

crossing the ridge itself when turning into the wind towards the landing site. In all

but light wind conditions (less than 10 knots), one need only approaching from the

lee side of a ridge when landing on a saddle that has steep or high walls. In other

situations, an approach at up to 90° to the wind wi th a turn into wind at the site is

preferable. The turn should not require additional tail rotor thrust, so the direction of

the approach should be selected accordingly. An approach to a pinnacle in strong

wind conditions can be angled to avoid turbulence and downdrafts so that a steep

approach is not essential. Alternatively, the approach can be made from the upwind

side, as described for ridges.

There are some important points to constantly be alert for during pinnacle or high

point approaches.

(a) An absence of peripheral clues both ahead and laterally deprives the pilot of

information about the rate of the approach. Unless the site is familiar to a

pilot, a short trail approach is advisable.

(b) Turbulence is often pronounced on the lee side.


(c) Ground effect is slow to come into play and approaches should not be protracted

on the lee side of the pinnacle with resulting demands for high power.

(d) The slope of the surface of a pinnacle is not as easy to assess as sites with

adjacent ground features. Pilots should be prepared to abort landings where

slopes exceed undercarriage and mast/hub limits.

Pilots must ascertain (through adequate reconnaissance) the best method in which

the task can be completed and most importantly, to have a planned escape route.

Do not hesitate to use the escape route if things don’t work out the way they were

planned. Some experienced pilots wish they had obeyed this golden rule.

1.19 Useful or Effective Investigation Techniques:

1.19.1 None.

2. ANALYSIS:

2.1 The pilot held a private pilot licence and had the helicopter type endorsed. The pilot

was healthy and fit to undertake the flight on the day of the accident and had 397.6

total flight hours on the helicopter type. Records showed that the helicopter was

certified, equipped, and maintained in accordance with existing regulations and

approved procedures. The helicopter was operated within its weight and balance

limits as well as when hovering in and out of ground effect. The helicopter had flown

a total of 26.1 hours since the last annual inspection was performed. This

unsuccessful flight took approximately 18 minutes and post examination of the

helicopter did not identify any deficiencies with the flight controls nor the engine that

could have contributed to the accident.

2.2 The pilot overflew Cradock Mountain and commenced the approach south easterly

towards the identified suitable landing spot on the mountain peak. On approach, the

pilot decelerated the helicopter and went into hover. During the process, the low

rotor RPM/blade stall light came on and the annunciator horn sounded. As a result

the helicopter drifted and landed hard on the slope damaging the skids/lower

fuselage area. The investigation determined that the accident was because of

downdraft the helicopter experienced during landing on the peak. The pilot, upon

entering the area could have expected higher engine power requirements to

maintain altitude.


2.3 His attempt to maintain altitude by increasing rotor pitch likely demanded engine

power beyond the helicopter’s capability, resulting in a loss of rotor rpm. In a

nutshell, the pilot attempted a landing where the power required exceeded the

power available. Mountain flying had opened up opportunities for general aviation

pilots to interesting destinations, and above all spectacular viewing of diverse

landscapes, yet it is a calculated risk where exposure to hazards can compromise

the safety of the flight. It also requires the understanding of the nature of flight, the

limitations of the helicopter, the limitations of the pilot and the procedures and

techniques to be followed. It should be well understood that there is a narrow

window of safety that an untrained pilot can easily stray out of, without the

experience and knowledge gained from a recognized training program and a

mountain checkout by a qualified mountain flight instructor.

3. CONCLUSION:

3.1 Findings:

3.1.1 The pilot was the holder of a valid private pilot’s licence (helicopter) and had the

helicopter type.

3.1.2 The last MPI prior to the accident was certified on 20 November 2014 by AMO No

1263 at 936.2 airframe hours.

3.1.3 The helicopter had flown a further 26.1 hours since the last MPI was certified.

3.1.4 Weather conditions were fine at the time, with a reported temperature at the around

the accident site was 20°C. The wind was south-east erly.

3.1.5 The calculated density altitude at the time was 6 567 feet AMSL (above mean sea

level).

3.1.6 The take-off weight of the helicopter was within its maximum certified take-off limit

of 2 500 pounds.

3.1.7 The out of ground effect (OGE) performance graph indicates that the helicopter was

below its maximum take-off weight.

3.1.8 The accident was considered survivable.


3.1.9 The pilot had no mountain flying course.

3.2 Probable Cause/s:

3.2.1 Poor technique.

4. SAFETY RECOMMENDATIONS:

4.1 None.

5. APPENDICES:

5.1 Rotor Stall:

Principles of helicopter flight by WJ Wagtendonk, page 164.

• According to the investigation, this R44 Raven II helicopter had experienced

what is known as a rotor stall due to downdraft condition. When the

helicopter is engaged in a powered descent, it experiences a rate of descent

flow in opposition to the induced flow across the disc. Inflow angles are

reduced and the blades’ angles of attack increase. The root sections of the

blades historically have the weakest induced flow.

• During a powered descent, the rotor sections may find their angles of attack

increased such that they stall. The early rotor stall acts like the early stages

of a vortex ring state. Provided the pilot keeps enough power to maintain

rotor RPM and provided the aircraft is flown in a manner that avoids the

development of vortex ring state, the descent continues normally. An

inexperienced pilot may pull more collective pitch to counteract the rate of

descent, not noticing or responding to the lowering of rotor RPM. If the pilot

fails to identify and react to the early rotor stall’s most prominent symptom,

decaying rotor RPM, then trouble is just around the corner. The correct

response to a development rotor stall is to increase the throttle to maintain

rotor RPM and lower collective simultaneously. Pilots flying helicopters

equipped with high-inertia rotors have more time to react than pilots flying

low-inertia rotor systems such as the Robinson R22.


• The decaying rotor RPM, brought on by the blade roots’ stalling, results in

less total rotor thrust, which increases the helicopter’s rate of descent. This in

turn increases the rate of descent flow and decreases the induced flow and

inflow angles further. The consequence is that the stalled region at the blade

roots spreads out towards the tips. Slower blade rotation means that

centrifugal force drops off sharply. Eventually, a complete rotor stall leads to

a loss of directional control, severe blade flapping, possible blade failure from

the coning angles, as well as nose-down pitch as the longitudinal stability

aligns the fuselage with the rate of descent flow.

5.2 R44 Raven II low rotor RPM emergency procedure: Pilot’s Operating Handbook

Page 3 to 10:

The Robinson R44's main rotor is considered a low-inertia rotor system. This type of

rotor has a tendency to deplete its stored energy quickly, leading to the decay of

main-rotor RPM. Engine power is transmitted to the main rotor through a belt

system, with the engine and transmission engaged through progressive tensioning

of the belts. When the main rotor ceases to be driven by the engine, the pilot must

quickly lower the collective to compensate for the rapid decay in RPM and

ultimately prevent an aerodynamic stall of the main rotor.

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