Thursday, September 23, 2010

Near mid-air over Minneapolis

From time to time I write here about aircraft accidents and, in particular, near misses. I usually hear pretty quickly -- at least at my day job -- from commercial pilots  who say it's no big deal. This shouldn't be one of those times.

The National Transportation Safety Board has issued this news release on what it classifies as a "near midair" over Minneapolis St. Paul.

The National Transportation Safety Board is investigating a near midair collision between a commercial jetliner and a small cargo aircraft that came within an estimated 50 to 100 feet of colliding near the Minneapolis-St. Paul Airport

On September 16, 2010, about 6:49 a.m. CDT, US Airways flight 1848 (AWE 1848), an Airbus 320, was cleared for takeoff on runway 30R en route to Philadelphia, Pennsylvania, carrying five crewmembers and 90 passengers.

At the same time, Bemidji Aviation Services flight 46 (BMJ46), a Beech 99 cargo flight with only the pilot aboard, was cleared for takeoff on runway 30L en route to La Crosse, Wisconsin. Weather conditions at the time were reported as a 900-foot ceiling and 10 miles visibility below the clouds.

Immediately after departure, the tower instructed the US Airways crew to turn left and head west, causing the flight to cross paths with the cargo aircraft approximately one-
half mile past the end of runway 30L. Neither pilot saw the other aircraft because they were in the clouds, although the captain of the US Airways flight reported hearing the Beech 99 pass nearby. Estimates based on recorded radar data indicate that the two aircraft had 50 to 100 feet of vertical separation as they passed each other approximately 1500 feet above the ground.

The US Airways aircraft was equipped with a Traffic Alert and Collision Avoidance System (TCAS) that issued climb instructions to the crew to avert collision. The Beech 99 was not equipped with TCAS and the pilot was unaware of the proximity of the Airbus. There were no reports of damage or injuries as a result of the incident.

NTSB and FAA investigators conducted a preliminary investigation at the Minneapolis airport traffic control tower on September 18th and 19th and are continuing to review
the circumstances of this incident.

In the past, when I've forwarded these reports of near mishaps, some pilots have suggested it's much ado about nothing. This is different. Fifty-to-100 feet in the clouds? That's a big deal.

To help you visualize these things, both planes took off on parallel runways, heading in the same direction. That happens all the time. Turning one plane into the path of another is highly unusual.

Update 11:55 a.m. - Here's the audio of the conversations that morning. The controller ordered the left turn -- to the south -- for the Bemidji flight as he gave the flight permission to take off. Normally, that turn would begin when about 500 feet off the ground, probably before the end of the runway. The turn would send the plane away from the parallel runway, where the US Air jet was also taking off.



A few minutes later, the controller asks the Bemidji flight if he's "in the turn." The pilot doesn't understand the question and asks for it to be repeated. It's not repeated. A minute or so later, the pilot asks to change frequencies to the departure controller and is granted the request. From the sound of things, that happened after the near miss. The controller asks, "why didn't you start the turn after departure?" The pilot's radio is nearly unintelligible, but I think he says, "forgot to go to departure," meaning he didn't change frequencies to the departure controller, which would have put him on the same frequency as the US Air flight.

Update 12:17 p.m. - As suspected, there were two planes on two different frequencies here. Here's the tape of the "departure frequency" when the US Air pilot (Known as "Cactus" because it's an Air West flight operating under the US Air colors) reports the near miss. The controller says he thought the Bemidji flight was going to go straight.



As with most disasters -- and near disasters -- this looks like the typical "chain of events," the breaking of any one of which -- repeating a question, repeating an instruction, knowing what each plan was for each airplane -- would've prevented it.

Of course, an investigation will take place, but this one isn't going to be hard to figure out. (Audio via LiveATC.net)

By the way, weather at the time was 0900 overcast and, of course, it was dark.

So what could have prevented this? File this under speculation but let's call it "informed speculation." On the tower tape, I did not hear either a request to change to departure frequency or an instruction to change to departure frequency. I don't know if that's even required (although I believe it is). But the tower controller asked two minutes after the La Crosse-bound flight took off whether the pilot had made the turn? That would indicate that the controller knew the guy was still on his frequency, wouldn't it?

The departure frequency indicates another problem. This incident occurred right at that moment when a pilot makes a transition from tower to departure. In fact, as you can hear, the US Air pilot asks "what's this guy doing off our left" before the departure controller confirms that he's got the US Air flight on his radar. That's a really icky time for things to fall through the cracks.

Update 5:30 p.m. - Here's my interview on Minnesota Public Radio's All Things Considered:

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