Narrative:

Aircraft X luaw on runway 22L waiting for wake turbulence delay from a runway 28C arrival. I advised aircraft X to be ready for an immediate in ten seconds. Aircraft Y was on two mile final for runway 28C when I cleared aircraft X for an immediate takeoff on 22L. Aircraft X did not roll expeditiously; and I felt that there might be an overfly by aircraft Y; so I canceled aircraft X's takeoff clearance and told him to hold in position. He had already pushed forward on the power and was starting his takeoff roll; so I told aircraft X to stop as soon as able. Observing aircraft X stopping abeam Y5 and clear of the 28C approach course; I allowed aircraft Y to land. I then taxied aircraft X down the runway; but mistakenly told him to turn at Y4 and hold short of 28C approach; which is not possible. Aircraft X questioned me on this; and; realizing my error; I told aircraft X to taxi to Y3 and turn right on Y; hold short of the 28C approach. As aircraft X exited 22L I realized that the turn northwest-bound onto Y was an illegal turn for an A321; so I issued alternate taxi instructions. Aircraft X did not hear the instructions and turned onto Y. I then taxied him back to runway 22L and he departed without further incident.the primary cause for me trying to depart this aircraft in a gap that was potentially too tight was the delay the aircraft had already incurred by waiting for wake turbulence from two 28C heavy arrivals; and the further delay he would take if he waited for aircraft Y and the next 28C arrival. With the wind at 210@09; the chances are very high that any wake turbulence would be blowing to the northwest; and that a 22L departure would not encounter it before rotation; but we do not have any metrics to determine this. All we have is a hard and fast rule that requires a two minute wake turbulence delay. This has been an issue since 28C opened; but ord cannot seem to get anyone to analyze the wake turbulence issues between these two runways. As a result; when long strings of minimally separated heavy jets land 28C; runway 22L departures can take substantial delays.in the past there have been significant wake turbulence studies done at various airports to determine the effects of between multiple runways. An issue was recognized between 28C heavy arrivals and 22L departures within three months of 28C opening over three years ago. However; nothing has been done to analyze the conditions that cause wake turbulence to be a factor at 22L; even though safety and efficiency can be substantially improved with a better understanding of the issue. I recommend that a study be conducted to find out the specific details that make wake turbulence a factor for these two runways.

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Original NASA ASRS Text

Title: ORD Tower Controller reported an unsafe operation when he realized that a departing aircraft needed to stop or a loss of separation would occur. The aircraft then taxied onto a taxiway that this type of aircraft was not supposed to be on.

Narrative: Aircraft X LUAW on Runway 22L waiting for wake turbulence delay from a Runway 28C arrival. I advised Aircraft X to be ready for an immediate in ten seconds. Aircraft Y was on two mile final for Runway 28C when I cleared Aircraft X for an immediate takeoff on 22L. Aircraft X did not roll expeditiously; and I felt that there might be an overfly by Aircraft Y; so I canceled Aircraft X's takeoff clearance and told him to hold in position. He had already pushed forward on the power and was starting his takeoff roll; so I told Aircraft X to stop as soon as able. Observing Aircraft X stopping abeam Y5 and clear of the 28C approach course; I allowed Aircraft Y to land. I then taxied Aircraft X down the runway; but mistakenly told him to turn at Y4 and hold short of 28C approach; which is not possible. Aircraft X questioned me on this; and; realizing my error; I told Aircraft X to taxi to Y3 and turn right on Y; hold short of the 28C approach. As Aircraft X exited 22L I realized that the turn northwest-bound onto Y was an illegal turn for an A321; so I issued alternate taxi instructions. Aircraft X did not hear the instructions and turned onto Y. I then taxied him back to Runway 22L and he departed without further incident.The primary cause for me trying to depart this aircraft in a gap that was potentially too tight was the delay the aircraft had already incurred by waiting for wake turbulence from two 28C heavy arrivals; and the further delay he would take if he waited for Aircraft Y and the next 28C arrival. With the wind at 210@09; the chances are very high that any wake turbulence would be blowing to the northwest; and that a 22L departure would not encounter it before rotation; but we do not have any metrics to determine this. All we have is a hard and fast rule that requires a two minute wake turbulence delay. This has been an issue since 28C opened; but ORD cannot seem to get anyone to analyze the wake turbulence issues between these two runways. As a result; when long strings of minimally separated heavy jets land 28C; runway 22L departures can take substantial delays.In the past there have been significant wake turbulence studies done at various airports to determine the effects of between multiple runways. An issue was recognized between 28C heavy arrivals and 22L departures within three months of 28C opening over three years ago. However; nothing has been done to analyze the conditions that cause wake turbulence to be a factor at 22L; even though safety and efficiency can be substantially improved with a better understanding of the issue. I recommend that a study be conducted to find out the specific details that make wake turbulence a factor for these two runways.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.