A Near-Disaster At Houston-Hobby

Photo by Ken Lund from Reno, Nevada, USA, CC BY-SA 2.0 , via Wikimedia Commons

I wrote about the epidemic of aviation near-misses back in August, but what happened Tuesday in Houston wasn’t a miss. Two business jets collided at the downtown Houston airport in what could have been a major disaster. Thankfully, both planes were able to get back on the ground with no injuries.

The accident occurred on Tuesday, October 24, at about 3:20 p.m. local time at Houston-Hobby Airport (KHOU). Hobby was my home base for the five years or so that I flew for a flight department in Texas, and it is a very congested and busy airport that is nestled in very busy and congested airspace with a multitude of other nearby airports. A Southwest Airlines hub, Hobby services a combination of airline and general aviation traffic.

This accident seems very similar to one of the previous near misses that occurred in Boston earlier this year when a private jet took off without a clearance. In that incident, the pilot said that he thought he had heard the tower controller issue a takeoff clearance rather than the actual clearance to line up on the runway and wait for permission to take off.

The Houston incident seems to be exactly the same. In a statement posted to the platform formerly known as Twitter, the National Transportation Safety Board said that the crew of a Hawker 850XP (N269AA) was instructed to line up and wait on runway 22. Instead, the Hawker began its takeoff roll and its wing struck the tail of a Cessna Citation Mustang (N510HM) landing on runway 13R.

The Hawker continued its takeoff and was subsequently vectored back around for an emergency landing. In audio of radio communications after the collision, one of the pilots of the Hawker replies to clearance from ATC, saying, “We just had a midair, we can’t do that.”

“You say what?” the controller asks.

The pilot then shows his unawareness of their violation by blaming the controllers, answering, “Yeah, somebody just, uh, you guys just cleared somebody to take off or land and we hit them on the departure.”

After this exchange, the controller then gives the pilot a vector to return to the airport. The crew was able to land the damaged plane safely.

Photos online show a chunk of the Citation’s tail cone missing immediately aft of the engines. The Hawker’s left wingtip appears damaged with part of the winglet, the vertical part of the wing at the tip, missing.

The crew and passengers of both planes are extremely lucky to walk away from this one. A matter of a few more inches might have severed the Hawker’s wing rendering it unable to fly while several additional feet might have meant a fireball that engulfed both planes.

You might wonder why airplanes were landing and departing on different runways at the same time. The answer is that it’s efficient.

Small, congested airports frequently have several runways in use when the weather allows. Often, one runway will be used for departures while a different runway will be used for arrivals. This allows the controllers in the tower to maximize the flow of traffic.

Sometimes these runways intersect. When this is the case, the tower controllers have to make sure that the airplanes are staggered so that only one runway is in use at a time. The “line up and wait” clearance allows the controller to save time by pre-positioning the departing aircraft to take off immediately after the landing aircraft rolls clear.

In this case, the controller’s plan was probably to have the Citation land on 13R and, when it passed through the intersection, to clear the Hawker for takeoff on 22. It’s a simple scenario that probably happens at least a thousand times every day.

The problem was the Hawker pilots misheard the clearance. Instead of waiting for the go-ahead, they started their takeoff roll and reached the intersection of the two runways at exactly the same time as the Citation.

There are attempts to make the system fail-safe. One method is to have two pilots in the cockpit. In theory, at least one of them should have heard the controller correctly. In the case of a disagreement over what their clearance was, the crew should have queried the controller to obtain clarification.

A second method is in requiring clearances to be repeated back to the controller. Audio of the takeoff clearance is not available at this time, but it will be interesting to see exactly what was said in the moments prior to the collision. Did the controller give the correct clearance? Did the pilot read it back? Did the controller catch the error? I’m sure that ATC tapes as well as the cockpit voice recorder in the Hawker will yield more details about what happened and why.

Additionally, the NTSB will also be looking at the duty times and recent activities of the accident crew. Had they been flying a lot? Were they fatigued? Had they had previous problems?

The two instances this year (that we know of) of airplanes taking off without a clearance are not the first. In fact, one of the worst aircraft accidents of all time was caused by a similar mistake.

In 1977, two 747 jumbo airliners collided on the runway at Tenerife in the Canary Islands. It remains the deadliest crash in aviation history and it was caused by a KLM pilot who erroneously thought he was cleared to take off even though a Pan Am airliner was still on the runway.

It’s difficult to say where we go from here, but not taking off without a clearance is a pretty basic aviation skill. If the facts of the case are as they appear to be, some pilots need to get back to basics.