LANCASTER, TENN. — A U.S. Marine helicopter may have narrowly averted disaster here last weekend after severing a pair of static lines along a high-voltage TVA transmission system in the vicinity of Center Hill Dam.
The system was in fact out of service at the time and therefore not carrying a charge, according to TVA officials.
The incident occurred around mid-morning on Saturday. Residents in the area heard and observed at least one military whirlybird flying low to the terrain above wooded hills and hollows not far from the Caney Fork River, about a mile downstream from the Corps of Engineers dam in northern DeKalb County.
The aircraft was reported by a Marine Corps spokesman to be an AH-1W SuperCobra attack helicopter. Its estimated value is more than $10 million.
The helicopter collided with the TVA lines along a 1400-foot span between two rugged hilltops a short distance from Highway 141. It was able to continue flying.
An investigation is ongoing, according to Marine Lt. John Roberts, a public affairs officer. He said the helicopter was, at the time of incident, returning to its base at Marine Corps Air Station New River near Jacksonville, N.C. following a training exercise.
“Why they were flying so low, that’s a valid question as part of the investigation,” said Roberts. “We will figure out exactly how they got into that situation, why they were there, if there was something else going on.”
The cost of repairing the helicopter is yet unknown, he said. “Obviously we can assume there was damage to it, but we just don’t know the extent of that damage,” said Roberts.
There are five lines linking the transmission towers. The two uppermost cables are parallel-running “nonelectrical” static wires designed to protect the system against lightning strikes.
The entire transmission line was under repair at the time, so no electricity was flowing through the system, said Jim Hopson, TVA public relations manager.
Hopson said there’s been no formal tabulation on the cost of damages, but the Marine Corps will likely get the bill ultimately.
“The way this works is that we typically do expect the agency that caused the damage to reimburse us for cost associated with repair,” he said.
A dispatcher at DeKalb County Emergency Communications in Smithville took a call around 6 pm Saturday from a Marine captain reporting the wire strike. TVA crews began inspecting the damage Sunday night.
A Marine helicopter was observed circling the site of the incident on Monday morning.
Neither the Federal Aviation Administration nor the National Transportation Safety Board is investigating. Media relations contacts for both agencies said the United States military investigates all accidents and incidents involving its own aircraft.
The helicopter may have been outfitted with with special wire-cutting devices, which helped avert a serious accident. “Wire strikes…account for about 5 percent of all civil and military helicopter accidents,” according to a 2008 FAA report on the effectiveness of wire-collision protection systems.
Matt Zuccaro, president of the Virginia-based Helicopter Association International, said wire-cutters can prevent “catastrophic results” by “eliminating the possibility that you will get tangled up in the wire.”
“There is also technology that actually detects the wires,” Zuccaro said.
However, the best course of action for pilots to keep clear of power lines is to maintain a safe altitude above them, he said.
“The primary safety protocol for avoiding wires is not to be down at the elevation of the wire environment to begin with,” said Zuccaro, who has nearly 50 years experience flying helicopters, including in Vietnam and as an Army flight instructor. “We recommend that when helicopters are in operation they be up at a satisfactory cruising level — which normally might be at least 1500 feet on an average flight.”
Zuccaro said he expects a full inquiry into the incident. “The military is very good about investigating all incidents and accidents, and they have a very good safety program,” he said.
“The primary question is — and we ask this question all the time ourselves –Why was the aircraft at the altitude it was when it encountered the wires?” he said. “It is either going to be mission-related, or it is going to be another reason that brings to question, Why was the flight operating at that altitude?”
In 2009, a Marine helicopter flying from California to North Carolina struck TVA power lines in White County near Rock Island State Park. The craft was forced to make an emergency landing after offloading 600 gallons of fuel, according to news reports.