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Avoiadable wirestrike in the middle of nowhere

  • This case study from the Avoidable Accident SeriesLow-level flying is a powerful reminder of low-level flight dangers.

Low-level flying aircraft

In November 2007, three German tourists, who had hired a Cessna 172N Skyhawk Aircraft as part of a contingent of three aircraft for an around Australia trip, were flying from Katherine to Tennant Creek in the Northern Territory.

There were no eyewitnesses to the accident, but the occupants of a car that was travelling on the Stuart Highway reported seeing the aircraft flying low above the highway moments before the accident. The witnesses recalled seeing an aircraft that was flying about 4 to 5 km to the west of the highway, about 150 ft above ground level. The Cessna made a slow, deliberate turn to line up with the highway, before it disappeared from sight behind a crest in the highway some distance in front of them. Shortly after, they saw the wreckage beside the highway.

Another wirestrike

The aircraft’s tail section hit a powerline that spanned the Stuart Highway, breaking the tail, which rendered the aircraft uncontrollable. The aircraft impacted the highway in a steep nose-down attitude and came to rest upside down about 150 m from the point where it had impacted the powerline. The aircraft was destroyed and the accident was not survivable.

Investigation of the aircraft wreckage determined that the aircraft’s ground speed at the time of the accident was at least 72 kts. The powerline involved in the accident was only 49 ft (15 m) above the road surface.

Before you decide to conduct low-level flying, ask yourself whether there is a legitimate or operational reason for you to do so.

Conscious decision to fly low

Evidence from images and video footage recovered from cameras found among the wreckage, suggests that there was a history of low flying by the group. One week before the accident, camera images show that the aircraft was flown low along a Western Australian beach by the same occupants with the pressure altimeter indicating an altitude of 70 ft above sea level. Video footage showed the aircraft flying below 100 ft along the beach for about 5 minutes.

Examination of the wreckage and previous pilot behaviour suggested that the pilots made a conscious decision to fly low, and were not conducting a forced landing at the time of the accident.

Earlier low flying by the group of tourists

Two of the three occupants held German private pilot licences and were sitting in the front seats. Neither of the pilots were approved to conduct low-level operations, and there was no evidence that either had undertaken any low-level flying training. Without approval to fly low and with no low-level training, the pilots probably had limited awareness of the hazards associated with flying low, such as impact with powerlines. Considering the remoteness of the area where the accident occurred, the pilots may not have expected to encounter man-made obstaces.

Safety message

Don’t forget that powerlines can be anywhere — even in the desert.

Don’t give in to the temptation to get down low for a better view of the scenery. Passengers may request you to fly lower but they probably don’t understand the risks. As the pilot, you are the one who needs to set the height limits.

Conclusion

Low-level flying is inherently unsafe for a number of reasons, so it should be avoided at all costs when there is no operational reason to do it (regardless of whether you have been trained and/or approved to do so).

Flying at low level is unsafe because:

  • there are more obstacles to avoid, many of which are hard to see until it is too late (e.g. powerlines and birds)
  • pilots have a higher workload because there are more hazards to negotiate in the environment
  • there may be turbulence and windshear that pilots do not encounter at higher levels and
  • there is very little time to recover control of the aircraft if something goes wrong.

From the accidents described in Avoidable Accidents - Low-level flying, it is apparent that the two major hazards of low flying are wirestrikes and pilots’ reduced opportunity to recover their aircraft from a stall or loss of control.

It is important to keep in mind that powerlines also exist in remote areas where you least expect. For example, the pilots of the Stuart Highway accident probably did not expect powerlines in the remoteness of the Northern Territory.

The effects of wirestrikes at low level are obvious — significant damage to the aircraft, usually leading to a loss of control and, because of the lower margin for recovery, subsequent impact with the ground or water. Pilots must keep in mind that not only do powerlines exist at low levels and in remote areas, they are also not easy to identify.

Even against a clear blue sky, wires are difficult to spot for a number of reasons. Wires can oxidise to a blue/grey tinge and may blend into the background, or the wire may be obscured by terrain. Single wires are difficult to detect from the air and can be encountered in the most unexpected places in rural areas. Even if a pilot has spotted a powerline, his or her ability to judge its distance from the aircraft can be distorted by optical illusions or a lack of nearby visual reference points.

Pre-flight assessment and planning is an important part of any flight. Make sure you have maps of your intended flight path with you when you fly, and study them before you get into your aircraft to identify any terrain, wire, or other obstacles that you need to avoid should operational circumstances necessitate flight at low level. If you have been trained and are qualified for low flying, and low flying is necessary, ensure that you conduct an aerial survey of the area from an appropriate height before you conduct any low flying.

Low-level flying also presents fewer opportunities to recover from a loss of control compared to flight at higher altitudes. It takes time to react and to regain control of an aircraft, and the closer to the ground you are, the less time and distance you have.

Flying at low altitudes is not only risky when things are going right; it becomes downright perilous when things are going wrong.

Before you decide to conduct low-level flying, ask yourself whether there is a legitimate or operational reason for you to do so.

 

More about Avoidable Accidents - Low-level flying

 

 General Aviation SafetyWatch video

 
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Last update 02 June 2016