Thank Goodness For TCAS

Modern Airliners are equipped with a device called a Traffic Collision and Avoidance System or TCAS for short. It's actually an amazing system that alerts pilots to the presence of other planes that could cause the potential for collision. The more advanced versions of TCAS even allow the systems in each plane to 'talk' to each other. If there is a potential for a collision, the system on one plane will tell it to climb whereas the system on the other plane will tell it to descend - thus avoiding a collision.

A TCAS display - the diamonds are other aircraft

In fact, today pilots are taught that no matter what your Air Traffic Control Clearance is, if the TCAS tells you to do something, you follow its commands. There was a tragic accident in 2002 where a controller told an aircraft to descend whereas the TCAS told it to climb. The pilot followed the controller's instructions which led to a mid-air collision.

The other day over Indiana, there was a near miss. This time however, both pilots followed the TCAS instructions and everybody was ok.

Cockpit device narrowly averts collision

Controller error undone by cockpit alert over Indiana
By Jon Hilkevitch | Tribune transportation reporter
November 15, 2007

A Chicago-bound jet came within seconds of a midair collision at 25,000 feet over Indiana, but a cockpit safety device alerted the pilots flying the other plane of the danger ahead, officials said Wednesday.

The near collision Tuesday evening was attributed to an error by an air-traffic controller who directed an eastbound Midwest Airlines plane to descend into the path of a westbound United Express jet, according to a preliminary investigation by the Federal Aviation Administration.

The controller, a 26-year veteran, appeared to have forgotten about the United Express plane after he mistakenly removed its electronic identification tag from his radar screen in preparation to hand off the plane to controllers in a different air sector, officials said.



The incident occurred "on the tail end of a rush" amid a shift change at the Chicago Center radar facility in Aurora, said FAA spokeswoman Elizabeth Isham Cory.

It was the latest in a series of serious errors since Oct. 1 at the FAA center, where tensions are high between the controllers union and management over adequate staffing levels.

The near collision occurred near Ft. Wayne, Ind., as the two regional aircraft closed in on each other at a combined speed of more than 700 m.p.h. -- or about 12 miles every minute, officials said.

The jets' speeds normally would have been even faster, but traffic in the airspace was slowed by congestion at O'Hare International Airport, where the United Express plane, carrying 28 passengers, two pilots and a flight attendant, was heading from Greensboro, N.C.

Tragedy was prevented when a collision-avoidance alert sounded in the cockpit of the Midwest plane, carrying 21 passengers, two pilots and a flight attendant from Milwaukee to Dayton, Ohio. The pilots executed an emergency climb to steer clear of the other plane, officials said.

"If they didn't suddenly climb, there would have been a convergence," said Midwest spokeswoman Carol Skornicka.

On radio communication tapes, the pilots mentioned three times how close the planes came to one another, said Jeffrey Richards, president of the National Air Traffic Controllers Association at Chicago Center.

"Center, you really lined us up on that last clearance," Richards quoted one of the pilots as saying.

The two aircraft came as close as 1.3 miles from each other horizontally and 600 feet vertically, the FAA said. The minimum separation permitted is 5 miles horizontally and 1,000 feet vertically.

"The controller at first did identify the potential conflict and took action" to stop the descent of the Midwest plane, Cory said. "However, it's still to be determined why, within less than a minute, he then dropped the data block [from his radar screen] and continued the descent."

The controller error marked the third serious mistake in only six weeks by controllers at Chicago Center, which handles high-altitude traffic over portions of the Midwest. Only one error of such magnitude occurred within the previous 12 months at the radar facility, officials said.

On Tuesday night, controllers on average worked close to the two-hour limit on their radar positions between rest breaks, Richards said.

"These controllers are fatigued from working such long stints and very few breaks compared to just three years ago," said Richards, who contends that a wave of retirements is draining the FAA of seasoned controllers.

Richards said the controller who committed the error was nearing the end of his shift and had returned from a break just several minutes earlier.

"Each of his sessions were right up to the two-hour limit," Richards said.