Sfo controller described a possible rule infraction. Traffic cleared for take off on runway 1L; rota...

Narrative:

I was working local control; landing runways 28; departing runways 01. Aircraft X; B762; was requesting runway 28L for departure. I departed aircraft X off runway 28L. Aircraft X rotated before the intersection of runway 01L. I cleared aircraft Y for take off on runway 01L; anticipating that the aircraft would not rotate before the intersection; therefore projecting the flight paths would not intersect. My local assist also agreed with this projection as we discussed it before I had cleared aircraft Y. It appeared aircraft Y started to rotate at the intersection of runway 28L. I think the two minute rule stating a projected flight path is rather vague. I will not clear an aircraft for take off based on my 'projections'; but instead just wait two minutes regardless of what I anticipate aircraft performance to be. Projections are just that and sometimes aircraft rotate at different points obviously based on numerous variables.

Original NASA ASRS Text

Title: SFO Controller described a possible rule infraction. Traffic cleared for take off on Runway 1L; rotated prior to the intersection of Runways 28L and 1L. Immediately after aircraft had departed Runway 28L; the reporter noting the rule covering this operation is somewhat vague.

Narrative: I was working Local Control; landing Runways 28; departing Runways 01. Aircraft X; B762; was requesting Runway 28L for departure. I departed Aircraft X off Runway 28L. Aircraft X rotated before the intersection of Runway 01L. I cleared Aircraft Y for take off on Runway 01L; anticipating that the aircraft would not rotate before the intersection; therefore projecting the flight paths would not intersect. My local assist also agreed with this projection as we discussed it before I had cleared Aircraft Y. It appeared Aircraft Y started to rotate at the intersection of Runway 28L. I think the two minute rule stating a projected flight path is rather vague. I will not clear an aircraft for take off based on my 'projections'; but instead just wait two minutes regardless of what I anticipate aircraft performance to be. Projections are just that and sometimes aircraft rotate at different points obviously based on numerous variables.

Data retrieved from NASA's ASRS site as of July 2013 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.

Attributes
ACN	991825
Time
Date	201202
Local Time Of Day	1801-2400
Place
Locale Reference	SFO.Tower
State Reference	CA
Environment
Light	Night
Aircraft 1
Make Model Name	B767-200
Operating Under FAR Part	Part 121
Flight Phase	Initial Climb
Route In Use	None
Flight Plan	IFR
Person 1
Function	Local
Qualification	Air Traffic Control Fully Certified
Events
Anomaly	ATC Issue All Types Deviation - Procedural Published Material / Policy

Sfo controller described a possible rule infraction. Traffic cleared for take off on runway 1L; rotated prior to the intersection of runways 28L and 1L. Immediately after aircraft had departed runway 28L; the reporter noting the rule covering this operation is somewhat vague.