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January 16th 2014 print

Geoffrey Luck

Down To The Wire

A novice aviator's encounter with powerlines very nearly the robbed the world of a lauded ABC journalist and, these days, a frequent critic of his former employer. Other pilots are not so lucky

plane in wiresNothing – absolutely nothing else sends a spear of terror through a pilot’s body like the sudden sight through the windscreen of a set of powerlines. Fractions of a second can measure the gap between life and oblivion. Yet in that instant the pilot instinctively knows – his mind calculating at computer-speed – all the mistakes he made in the last several minutes, or even longer, which now place him precisely on a path where he may crash and burn.

Just like the minutes of meetings where nobody wants what really happened remembered, log book entries tend to the laconic. So this one of RAAF Cadet Pilot Officer O15187 reads:

1.6.52: VH-AYW   –  More forced landings practised from 3000 ft. First 6   — OK. Hit E.L. wires on 7th approach.

“Hit” was a considerable under-statement. I fairly chewed through them. Three 7-strand copper cables, carrying 415 volts to a farmer’s dairy, only seven metres above the ground. But I survived. Because the one thing I did right that day was to push the throttle wide open the moment I saw that I wasn’t going to clear them. The Gipsy Major roared immediately to 2000 revs. AYW, my favourite Tiger Moth in the aero club fleet, responded magnificently. She jerked briefly like a thoroughbred racehorse released from the starting gate as her brass-edged wooden propellor sliced through the wires, then haughtily discarded a length from the last cable, flinging it away to wrap around the port interplane struts and slash a great piece of fabric from the port aileron. Then she climbed away and took me safely home, trailing wire and thoughts of excuses. “My boy” said the Chief Flying Instructor, “You must never try to stretch a glide. You’re bloody lucky to be alive.”

Accident analysis has shown that the best chance of survival is to hit wires with the propellor. The difference a few feet can make was demonstrated in October 2012 when a Cessna 172 landing at a private airstrip at Bagshot in Victoria hit powerlines at the southern end of the runway. The nosewheel tripped on the wires, flipping the plane upside down; it crashed and was burnt out. One passenger was killed, a second and the pilot were injured. (1)

Mankind’s greatest technical achievement, the heavier-than-air flying machine,  may soar far higher than the most powerful bird, but is far more vulnerable close to the ground, where the aviator’s are no match for avian eyes. Which is why aeroplanes keep running into things – mountains, trees, other aeroplanes, recently a ferris wheel in a village fair, and all too frequently, wires.

Australia is criss-crossed by millions of kilometres of wires and cables of every type, size and height above the ground. 74-thousand kilometres of high tension transmission lines gird the continent, sharing electric power back and forth between states and regions. The most dangerous for a pilot because they’re thick and carry very high voltages,  they are, quixotically often the most visible because of their pylons, marching across the countryside. But thousands of smaller wires, carrying lower voltages or telephone signals, usually strung between slender wooden poles, sometimes slung across gullies, rivers, gorges and roads, are almost invisible from above – or even alongside them.

Contrast my fortuitous outcome with these, taken at random from the reports of the Australian Transport and Safety Bureau:

On May 20. 2010, a Bell helicopter 206L LongRanger, registered VH-OSU, commenced forestry spraying operations about 37 kms SSW of Latrobe Valley Airport, Victoria. The final spray run resulted in the helicopter’s flight path crossing a powerline that was known to the pilot. The helicopter contacted the wire, seriously damaging its flight control system and main rotor mast, which likely rendered it uncontrollable. The helicopter subsequently impacted the ground. The pilot was fatally injured. The investigation found that it was likely that the pilot failed to recall the existence of the wire. The inherent difficulty of visually detecting the wire, combined with the operating groundspeed, meant that the pilot would not have had sufficient time to avoid the wire after seeing it. (2)

On April 10 2010, A Cessna 188B AgTruck, registered VH-JHR was being operated on a weed-spraying flight over a cane field about 13 km south of Ayr (N. Queensland). The aircraft was positioned to fly under powerlines that crossed the intended flight path at about 3.25m above the top of the crop. The aircraft, which is about 3.6m high, contacted the powerlines and severed the top of the aircraft’s fin and rudder horn. Control of the aircraft was lost and it collided with terrain shortly afterwards in a steep, nose-down attitude. The pilot was fatally injured. (The ATSB discontinued its investigation into the cause of the crash when the pilot’s post mortem examination revealed a high blood alcohol concentration.) (3)

On Christmas Eve, 2006, an Auster J1/A1, registered VH-ALO, took off from a private airstrip at Nelson, Victoria, with only the pilot on board. During the initial climb out, the aircraft was observed making a low-level turn towards two hangers where three people were standing to watch the departure. The aircraft was observed striking powerlines 12m above the ground in front of the hangers. The propellor was shattered, the engine stopped, the aircraft impacted the ground inverted, at a steep angle. The pilot was fatally injured. The ATSB report concluded: “It is at least possible and, on balance likely, that the pilot became focused on the execution of the low-level flight over the witnesses, and….forgot about the powerlines.” (4)

On November 10 2007, a Cessna 172N, registered VH-WLQ, with three German tourists – two pilots and a passenger on board departed Katherine, NT on a private VFR (visual flight rules) flight to Tennant Creek. The aircraft struck a powerline which spanned the Stuart Highway 15 m above the road, 20km north of Elliott. The aircraft’s tail section was broken rearwards from the aft fuselage, rendering the aircraft uncontrollable and causing it to impact the highway in a steep nose-down attitude. The three occupants were fatally injured. The investigation concluded that the pilot was not attempting an emergency landing. The descent to, and ongoing flight at a low level was probably as a result of a conscious decision by the pilots to fly below the legal minimum height of 500 ft. (5)

On September 25, 2010, The pilot of a Rockwell International 114 aircraft registered VH-CSH was attempting to land at Geelong after a flight from Moorabbin (Melbourne) along the Victorian coast. As the aircraft was about to cross the Surf Coast Highway, the pilot felt a jolt; the aircraft had collided with high-voltage powerlines before impacting the ground. The pilot and passenger escaped through the windscreen, the pilot with serious injuries and the passenger with minor injuries. The aircraft then caught fire, suffering serious damage. Since then the uncertified unregistered landing area at Geelong has been closed to visiting aircraft. (6)

On April 20. 2009, two helicopters were contracted to spray a pine plantation near Langkoop, Victoria, with fertiliser. When one did not arrive at the pre-arranged meeting place for lunch, the pilot of the second helicopter began searching and located the wreckage of VH-EZT, a Robinson R44 Raven in a paddock, near a powerline. The pilot was fatally injured. Recorded data from the helicopter’s satellite navigation system showed that the pilot did not conduct a reconnaissance of the unfamiliar area which may have alerted him to the presence of the previously-identified powerline. (7)

These accidents are representative of the two of the most vulnerable categories in  aviation – aerial agriculture and private flying. Between 1994 and 2004 the ATSB counted 119 wirestrike accidents. 169 people were involved, 45 died and 64 were injured, many seriously. (8) Seven years later, the Bureau  re-visited its accident database. Between 2004 and 2010, there were 130 reported wirestrikes. 93 of them involved fixed wing aircraft and helicopters involved in tasks such as crop dusting, mustering, surveying, photography and transmission line patrolling. (9) In 2011, the latest year for which data is available, there were 32 accidents. 21 involved fixed-wing aircraft, five helicopters and three hot-air balloons. 75% of the wirestrikes involved operations where low flying was a normal occupational hazard. (10) This accident rate (as a proportion of the total number of aircraft on the register) is many times greater than in the U.S. Helicopters suffered a disproportionate share of the accidents.

At least eight of the accidents on that list were not reported at the time, and were identified only as a result of information from the electricity companies. (11)

Wirestrikes resulting in death or injury, or serious damage to the aircraft are the only ones we know about. Many lucky escapes are going unreported. Between July 2003 and June 2011, 40%  of such incidents were not reported to the ATSB. The Bureau detected them by working backwards from damage to powerlines discovered by electricity authorities for unexplained reasons. The aircraft involved were never identified. As a result of these shocking findings, the Bureau recommended changes to the Transport Safety Investigation Regulations, requiring that all contacts with a wire during flight must be reported. At the time of writing, wirestrike has not yet been added to the list of reportable matters. (12)

One such escape is known and has been publicised as a salutary warning to pilots. A Bell Long Ranger helicopter on a fire-bombing mission in Victoria’s Bunyip State Forest was taxying in the hover to land on a creek flat when the pilot and the Fire Service Air Attack Supervisor on board saw the powerline simultaneously. The wire was UNDER the rotors and just above the cabin. The pilot carefully backed away; disaster was avoided by centimetres, probably only because the aircraft was travelling at less than 20 kph at the time. (13)

It’s now more than 50 years since Australia’s aviation authorities began to take wirestrike seriously. Aerial agriculture had boomed since the development of the first specialised aircraft – the Piper PA-25 Pawnee and the Cessna C-188 Agwagon – but their crash survivability, as measured on international scales which took account of airframe integrity, fire potential, pilot restraint systems and evacuation was half that of other aircraft.

As early as 1965 the then Department of Civil Aviation had ordered flexible rubber cells to be fitted inside the fuel tanks of the PA-25 to minimise the risk of post-crash fire. Between 1966 and 1971 DCA’s Airworthiness Branch studied wirestrike accidents in detail. It followed up with an eight-year programme to develop a wire-cutter device which was ready for manufacture by 1979, but it was never adopted. Cost, design defects and attachment problems proved it impractical. Bristol Aerospace Canada however developed a passive wire cutter for helicopters which has now been produced for almost every model and type. (14) Since 1992, every U.S. military helicopter has been fitted with a wire cutter.

In June 1991 the first comprehensive report on wirestrike accidents in Australia was compiled. It was provoked by an increase in accidents involving agricultural aircraft in the 1980s, when a total of 20 pilots died in 144 crop-duster crashes. Two-thirds of the planes were destroyed or damaged by fire after the crash. (15)

What happens when an aircraft hits powerlines? The report, by the Bureau of Air Safety Investigation  – the predecessor of the ATSB – explained:

“There is a transfer of kinetic energy into work done per unit time. Work done is defined as the amount of force required to displace the cable over a given distance. To successfully break the wire, the impacting aircraft must overcome the inertia of the cable to reach the point of maximum tension in the direction of motion. This requires a certain amount of force. Assuming rigid anchor points, a relatively short span will involve relatively less cable weight and require a correspondingly smaller force from the impacting aircraft to break the cable.” (16)

What that means is an aircraft has little chance of breaking a large thick high-voltage powerline, and will mostly likely be destroyed by it. This report was also the first to look closely at the two main aircraft types, the Piper and the Cessna. The report found Piper aircraft suffered more structural damage than Cessnas, but the higher tail of the Cessna was responsible for more misjudgements in straight and level flight (i.e. when flying under the wires).

BASI explained scientifically why it is usually safer to cut wires with the propellor:

“… propellor-cutting efficiency depends on the following factors: the transfer of high stored rotational energy from the propellor, high RPM, and extremely short time interval (msec) between the travel of two blades and the effectiveness of the leading edge profile as a cutting tool.”

The report imaginatively suggested that propellors could be improved by adding high-strength steel to the leading edge, or even embedding small quantities of explosive in the leading edge (presumably to blast the wires out of the way). Coming back to earth, it admitted: “Both improvements would require a completely redesigned propellor.”(17)

Agricultural aviation has a long history of death and disaster. The first recorded crash was in August 1919, when a U.S. Army pilot, Lt. William Tillisch and his Agriculture Department observer E.L. Diven, died while searching for violations of crop-control laws in southern Texas. The authorities were trying to stamp out an invasion of pink bollworms from Mexico, and had declared the state a cotton-free buffer zone. The previous year, poison dust had been dumped from a plane to kill the pink bollworms, but all records of this experiment have been lost. (18)

The world’s first recorded crop-dusting flight was made in August 1921 in a World War I biplane trainer, a Curtiss JN-6 ‘Jenny’. Army engineers strapped a crude hopper to the side of the plane, filled with 125 pounds of lead arsenate to attack an outbreak of catalpa sphinx moth in Troy, Ohio. Lt. John Macready flew his Jenny at 80 miles an hour at a height of 25 feet over the trees while his observer J.S. Hauser, a forest entomologist who had never flown before, cranked a handle to release the powder. The caterpillars died; crop dusting was born. (19)

By 1923, the Agriculture Department, with the co-operation of the Army’s Air Service had designed a more efficient hopper and carried out successful experiments against the cotton boll weevil at Tallulah, Louisiana. They produced a film, “Fighting Insects from Airplanes,” which excited post-war fliers of the early aviation companies about the commercial possibilities. One of the first of these, Huff-Daland Dusters Inc. set up operations in Georgia. It got full co-operation from the Army which released 12 pilots and 18 mechanics to staff the venture. By 1925 the company had dusted more than 60,000 acres with calcium arsenate, and was designing its own planes. The flatlands of the Mississippi delta proved ideal for the industry; Huff-Daland grew into Delta Airlines, the oldest American airline still operating today. (20)

World War II gave the industry an even bigger boost. In the late 1940s, thousands of surplus aircraft were available cheaply, and new chemicals – fertilisers, pesticides and weedicides – boosted aerial agriculture and crop yields. In Australia too, the industry took off. At first, DH-82 Tiger Moth trainers bought from war disposals were fitted with spray booms under the wings, and a tank for 330 lb of superphosphate in the front cockpit. They were dangerously under-powered for the work and suffered a high accident rate. Even the wartime Wirraway was re-designed as the CA-28 Ceres, although the Roman goddess of agriculture didn’t bring it much success. (21) By the 1950s, the Cessnas and Pipers took over; the two companies manufactured a total of 9,000 aircraft, used worldwide. Since then, larger more powerful aircraft – The Grumman AgCat, the Thrush Commander and the Polish Dromader have become the preferred types in Australia, with the Dromader being used also for water-bombing.

With the increasing use of helicopters, not only for crop dusting but also for other low-flying tasks, training pilots how to look out for wires has become a minor industry. Canadian Bob Feerst a veteran pilot travels the world running courses, explaining how to forecast the presence of wires long before they can be seen. He says:

“Pilots are notorious for thinking they’ll see the wire in time to avoid it. But wire is not always visible. You have got to start thinking about wire as an invisible hazard. The visibility of wire is affected by such diverse factors as its size and alloy, the background and the light angle: a wire that is perfectly visible from one direction may be completely invisible 180 degrees out. Wire can pass into and out of view in a matter of seconds.” (22)

One of the principles Feerst uses in his courses is ‘Heinrich’s Triangle’ a workplace accident theory of the 1920s that says for every serious accident there are 29 minor injuries and 300 unsafe acts. The concept has been discredited as statistically invalid in the modern industrial workplace, but Feerst uses it to warn how many times pilots may come close to disaster on the wires without learning to avoid them.

So why do experienced pilots – statistically the most accident-prone – continue to run  foul of wires that can kill them?  A former U.S. Civil Aviation Authority Examiner of Airmen, the late John Freeman believed the 70 degree human field of vision was the problem. That, combined with even a pilot’s good visual acuity meant that there were inherent visual traps in detecting something as fine as a wire. A pilot approaching wires between two visible poles would mostly be too far away to discern the wires, or too close to see both the poles at once. Clues within the field of vision would be outside the range of vision and vice versa. (23)

In the last few years the ATSB has been trying to drum this lesson into pilots with regular articles in its bi-monthly Flight Safety Australia magazine. Scouting the field before descending to the level where powerlines abound is vital, it advises. Distraction is the danger, it warns. The pilot may be distracted visually – by the task area, or the scenery; by the radio or mobile phone; by a control problem, or most seriously, suffer cognitive distraction – simply being ‘lost in thought’ or engrossed in the task. As more helicopters are used for everything from mustering cattle to servicing powerlines, the risks are rising.

When there is an accident, there’s often not much left of the plane or the pilot. I bought my prop with the series of nicks in it from the Royal Queensland Aero Club as a souvenir of my survival for £5, the same amount the Club paid to buy the entire plane from war disposals. You can now inspect it in the Camden Aero Museum.

Geoffrey Luck was an ABC Journalist from 1950 until 1976

 

References

 

1          ATSB Investigation AO-2012-142

2          ATSB Investigation Nr AO-2010-033

3          ATSB Investigation Nr AO-2010-026

4          ATSB Investigation Nr AO-200607801

5          ATSB Investigation Nr AO 2007-058

6          ATSB Investigation Nr AO 2010-071

7          ATSB Investigation Nr AO 2009-017

8          Wire-strike Accidents in General Aviation: Data Analysis 1994-2004

ATSB Transport Safety Investigation Report B2005/0055

9          ‘Watching the Wire’; ATSB Flight Safety Australia magazine Mar-Apr 2011

10        Aviation Occurrence Statistics 2002 to 2011 ATSB AR 2012-025  p.76

11        Aviation Occurrence Statistics 2002 to 2011  ATSB AR 2012-025  p.76

12        Under reporting of Aviation Wirestrikes ATSB Transport Safety Report

AR 2011-004

13        ATSB Flight Safety Australia Magazine Issue 88 Sept-Oct 2012

14        Wire Strikes: A Technical Analysis. Bureau of Air Safety Investigation

June 1991 ISBN 0 642 16248 4

15        ibid

16        ibid

17        ibid

18        Origins of Aerial Crop Dusting: Eldon W Downs & George F Lemmer

Agricultural History Vol 39 No 3 1965

19        ‘Farming in the 1940s’ ; Wessels Living History Farm, York Nebraska

20        Delta: The History of an Airline; W. David Lewis & Wesley Phillips Newton

Roots: From Crop Duster to Airline; The Origins of Delta Air Lines to World         War II; James John Hoogerwerf. Auburn University PhD dissertation 2010

21        Wirraway to Hornet: History of the CAC 1936-85; Brian Hill

22        “Bird on a Wire” Verticalmag.com 11.1.2012

23        “Flying at Lower levels – safety through awareness” – John Freeman 1995 Kent Town Wakefield Press)