One Frequency - Two Airplanes - Same Call-Sign

Pilots quickly learn to speak clearly, to say only what needs to be said and to pay close attention not only to what is being said to them, but to the communication between other aircraft and air traffic control as well. We refer to this as situational awareness...an awareness of what is going on round you. Accidents have been avoided and lives saved by pilots and controllers who paid close enough attention to those around them to identify mistakes and misunderstandings early enough to prevent disaster.

A few weeks ago, I began a three day trip with a short flight from Dallas to San Antonio, Texas. There was a passenger in every seat and a cockpit jumpseater along for the ride. The jumpseat is an extra seat in the cockpit intended for FAA observation of the flight crew, but when it isn't being used for that purpose, a pilot is allowed to occupy the seat for personal travel.  Sometimes, having an extra body in the cockpit is an annoyance, especially on long flights, but the up side is an extra set of eyes and ears. 

We closed the cabin door and pushed away from the gate for an on-time departure.  As we approached the end of the runway, the tower cleared us for takeoff. "Flight 123, RNAV GVINE, runway 36R, cleared for takeoff."  It was my leg, so as we lined up on the runway centerline, I advanced the throttles. But before the engines had time to spool up, the captain reached up and pulled the throttles back to idle.  "We don't have a takeoff clearance" he said.  He misunderstood the clearance and thought we had been told to "line up and wait" on the runway. "Line up and wait" is a clearance to line up on the runway and stop until cleared for takeoff.

"Line up and Wait" 

I glanced over my shoulder at the jumpseater who I could tell had heard our takeoff clearance, but anytime there's confusion over a clearance, the thing to do is ask. I was about to clarify with the tower, but before I could get the words out, we overheard an aircraft on final approach call the tower.  "Tower, Flight 123, visual 36L," to which the tower responded "Flight 123, wind 330 at 15, runway 36L cleared to land."  Well now we were really confused.

Obviously, I'm not using the real call sign or flight number here, but there was a guy on final to runway 36L who had our exact call sign. Two airplanes...on the same frequency...one landing…one taking off...both with the exact same call sign. How could that possibly happen?

This was the first leg of a three day trip for me and my crew, but Flight 123 originated in another city earlier in the day.  Off the top of my head, I can't remember the actual details, but let’s say Flight 123 was scheduled to leave San Diego, California at 7am, but was delayed and didn't actually leave until 8.  Let’s say Flight 123 was originally scheduled to arrive in Dallas at 12 o'clock noon (two hour time difference), but due to the late departure, didn't actually land until 1pm. 

Flight 123 was a thru flight, originating in San Diego with a stop in Dallas before continuing to San Antonio.  The San Antonio flight (mine) was scheduled to leave Dallas at 1pm. The original plan was probably for the jet from San Diego flight to land at noon and continue on to San Antonio.  But the original flight was late, so the airline decided to use another aircraft in order to keep the operation running on time. 

Have I lost you yet?

Since this was the first leg of my trip, I knew nothing about the late arrival from San Diego, and the flight crew working the flight from San Diego to Dallas knew nothing about me.  My flight should have been identified as a "stubbed" flight and the flight number should have been changed.  Usually, this is accomplished by adding a letter to the end of the original call sign.  In this case my new call sign might have been Flight 123P. But somehow, the fact that these two flights would intersect was not noticed by anyone and my flight number was not changed.  

The captain set the parking brake right there on the runway.  He had no intention of moving the aircraft until we clearly understood the situation.  I'm a little surprised that the tower controller didn't chime in with some clarifying instruction at this point, but he didn’t.  Sometimes, I think we get so accustomed to the normal flow of things, that we don't notice slight irregularities.  So I keyed the mic and asked for clarification.  “Tower, Flight 123, please confirm we're cleared for takeoff on runway 36R.” 

There was long pause before we got response.  I'm guessing the guy in the tower was a confused as we were at that point.  He finally responded. “Flight 123...airborne on final to runway 36L...you are cleared to land.  Break.  Flight 123...on the ground on runway 36R...RNAV to GVINE, runway 36R, cleared for takeoff.”

I’m not sure exactly what went wrong or who was supposed to catch this, but I'm pretty sure it wasn't me.  At any rate, we were now confident in our clearance so I pushed the throttles up and away we went.  In hindsight, it would probably have been better to wait until the other Flight 123 had landed before we tookoff.  I can only imagine the confusion if the other flight had been forced to go-around and we had both been in the air at the same time.  Insert cliche about hindsight here...