News Cut: September 23, 2010 Archive

Near midair over MSP

Posted at 11:29 AM on September 23, 2010 by Bob Collins (26 Comments)
Filed under: Aviation

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 (see note below). 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.

The clearance and any conversation with the US Air plane is not on the tower tape (which I've edited and telescoped), raising the possibility that it was occurring on another frequency. I'll post that frequency tape in a moment.

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)

Update 3:08 p.m. I'll be on All Things Considered tonight to talk about this and Steven John asked me what could have prevented this. I don't have all the facts on this case so it's informed speculation at best. But as a pilot, there are a couple of things I noticed:

On the tower tape, I did not hear either a request from the LaCrosse-bound flight to change to the departure controller's frequency or an instruction to change to departure frequency. I don't know if that's even required (although I believe it is, I don't have my rulebook at work). 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 Bemidji pilot did not repeat the full clearance he got to take off, but he wasn't required to. Some of us private pilots like to repeat the whole thing (including the instruction to turn left), so that a controller can pick up on our mistake and correct it before it's a problem.

The departure frequency tape indicates another possible 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.

There's also a bit of confusion from the departure controller what instructions had been given to the La Crosse-bound aircraft.

Humans make mistakes. That's going to happen. The FAA will undoubtedly be looking at ways to break the chain of human mistakes that usually are the hallmark of any aviation disaster. Handing out any discipline, hopefully, will be secondary.

Update 5:21 p.m. - Here's my interview on All Things Considered:

7:50 p.m. - Very important point to consider from Dave Pascoe at liveatc.net:

One small thing to keep in mind in your analysis (which after a very quick read I think is right on the mark) - the receivers near KMSP scan between several frequencies. One scans both Tower freqs. The other scans several Approach/Departure freqs. So blocking can and does occur from time to time. It is important to understand that just because a transmission wasn't heard on the recording doesn't mean it didn't happen (like a readback or Tower switching an aircraft to Departure).

I mentioned earlier that there wasn't a repeat on the tape of the question about the lack of a turn. My guess is that was repeated and wasn't picked up.