Date: 201809
Local time of day: 1801-2400
Location: IAD.Airport, DC
Aircraft: Commercial Fixed Wing
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
ATC / advisory: Tower IAD
Second aircraft: Commercial Fixed Wing
Reporter organization: Government
Reporter function: Local
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Situational Awareness; Communication Breakdown
Second reporter function: Pilot Flying; Captain
Anomaly: ATC Issue All Types; Conflict Ground Conflict; Critical; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Flight Crew Rejected Takeoff
Contributing factors: Human Factors; Procedure
Primary problem: Procedure

Narrative: Aircraft X was given line-up and wait on Runway 19C and was told multiple aircraft will be crossing the runway down field. I then followed that transmission with a takeoff clearance with Aircraft X. Somehow; I did not remember giving a departure clearance to Aircraft X and proceeded to cross 2 aircraft across the runway. Those aircraft were Aircraft Y and Aircraft Z. Aircraft X stated that he was aborting takeoff clearance because Aircraft Z was given takeoff instructions. The pilot was correct and extremely professional about the entire situation.I did not recall clearing Aircraft X for takeoff. My strip management procedures was correct. The only recommendation I can make is turning the strip over if I am going to be crossing aircraft while having an aircraft in position and hold just slow the situation and force me to [be] extra cautious. We rarely use this operation; but it can be applied all of our operations.


Second narrative: After diverting to IAD due to thunderstorms at the original destination airport; taxiing towards the gate we were holding short of Runway 19C at Taxiway W4. I recall hearing Aircraft X flight being told to line up and wait on 19C and tower informing them that multiple aircraft would cross the runway in front of them. A short time after I recall being cleared to cross Runway 19C at W4; to hold short of Y; and to contact ground on the other side. After our readback I also heard an Air Carrier Y aircraft receive clearance to cross 19C at W2. Before entering the runway I looked to my left and noted that the left was clear; Aircraft X appeared to be in position; and we were cleared to cross the runway. I also noted the Air Carrier Y aircraft further down field that had also been cleared to cross the runway and appeared to be starting to move. From my vantage point it appeared Aircraft X was holding in position and I did not perceive the aircraft to moving. I did not hear that Aircraft X in position had received a takeoff clearance prior to our clearance to cross the runway. We cleared the runway and contacted ground control as we had been instructed by tower; and subsequently received clearance to taxi towards the gate and to contact ramp control.I was unaware of what had taken place until a week later when I received a call from my chief pilot to discuss an event that occurred at IAD. While meeting with my chief pilot he played the ATC tapes; where I learned that the controller had cleared Aircraft X to line up and wait and informed them multiple aircraft (ourselves and Air Carrier Y) would cross the runway in front of them. It was only after hearing this tape that I learned tower had cleared Aircraft X for takeoff; and then subsequently cleared our flight and the Air Carrier Y flight to cross the same runway. At the time of the incident I did not hear Aircraft X receive takeoff clearance before our runway crossing clearance; as the frequency was very busy. ATC did not inform us of what had taken place; nor did we receive any indication from ATC that anything unusual had occurred. We did not hear Aircraft X inform tower they rejected their takeoff for traffic on the runway; as we had already switched to ground control as we had been instructed. Upon listening to the ATC audio; I learned the controller cleared Aircraft X for takeoff; then a short time after cleared our flight and another flight to cross the same runway. While we did not hear the subsequent transmission during the flight; from the ATC tapes it appears that when Aircraft X informed the controller they had rejected takeoff for an aircraft on the runway; the controller had forgotten they had cleared Aircraft X for takeoff before they had cleared us to cross the runway. The tower frequency was very busy; so we did not hear Aircraft X receive a takeoff clearance or catch the controller's error.I believe both crews and ATC can always exercise greater vigilance when listening for and issuing clearances; particularly runway crossing and takeoff clearances and especially during busy operations and on congested frequencies; as greater workloads increase the chance of an error like this occurring. I also believe that there should be a review of line up and wait and runway crossing procedures; as having multiple aircraft on the same runway in different positions for different purposes increases the likelihood of an error like this being made. If departing aircraft could not enter the runway until receiving a takeoff clearance; or if crossing aircraft did not receive a crossing clearance until departing aircraft were clear of the runway or airborne; the chances of an incident like this occurring would be greatly reduced or eliminated.


Synopsis: IAD Tower Controller and flight crews reported a ground conflict at IAD airport.  Controller reportedly forgot about clearing an aircraft for takeoff and then clearing crossing traffic downfield on the departure runway.