Date: 201407
Local time of day: 1801-2400
Location: MSP.Airport, MN
Light: Night
Aircraft: Large Transport; Low Wing; 2 Turbojet Eng
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Taxi
ATC / advisory: Tower MSP
Second aircraft: Large Transport; Low Wing; 2 Turbojet Eng
Reporter organization: Government
Reporter function: Local
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Confusion; Distraction
Anomaly: ATC Issue All Types; Conflict Airborne Conflict; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Ground Incursion Runway
Detector: Person Flight Crew
When detected: Taxi
Contributing factors: Aircraft; Procedure; ATC Equipment / Nav Facility / Buildings
Primary problem: Procedure

Narrative: I was working Local South combined with Local West.  The configuration was landing and departing RWY 30R and RWY 30L and also departing RWY 17.  The traffic volume was moderately high; but I knew it would slow down relatively soon.  There were several aircraft on final to RWY 30L with one or two departures waiting for the same runway; and several (3-5) aircraft staged down field at intersections to cross RWY 30L en route to RWY 17.  I also had a few departures already waiting at RWY 17.  Aircraft X was holding short of RWY 30L on RWY 22; and Aircraft Y was short final to RWY 30L.  I felt like I was busy and in order to keep traffic moving; I was just making one transmission after another without allowing any 'dead' air time. I scanned RWY 30L while making the previous transmission; then keyed up and told Aircraft X; 'On RWY 22 cross RWY 30L join Whiskey to RWY 17.'  As soon as I un-keyed the mic; the pilot immediately replied unable.  I also immediately realized that Aircraft Y was just touching down.  Even if Aircraft X had not said anything; I did realize my mistake in time to prevent an error from occurring.  The problem for me in this case is actually the layout of the Tower cab window pillars.  The Local South position cannot see the approach end of RWY 30L without moving several feet right; unable to move left because Ground South is right next to Local South.  I'm sure I would have had more time to thoroughly scan the runway if Local West had been split off; but I am also very comfortable working that level of traffic with them combined.   I thought about this a lot after it happened.  The potential still exists for this situation to happen again; even during low periods of traffic volume.  Because of the blind spots I try to remember to work Local South a few steps further right; or even from the adjacent position of Ground West (which is rarely opened).  Then I began thinking about the best way to really keep this from happening again.  I only came up with one idea which I think is good enough to share.  We already have ASDE-X and associated RWSL's at intersections; would it be possible to wire a small red LED light into all the Local Control positions strip bays; and link it to the RWSL's?  That way when the RWSL's are activated the LED light would come on and indicate that the runway is unsafe to cross/enter; regardless of any blind spots we might have.  It wouldn't even have to be very bright; but I feel something like that would be such a quick and efficient reminder to not cross; or approve any other runway operations.




Synopsis: MSP Tower Controller tells an aircraft to cross a runway by using a runway and the pilot refuses instructions.  Controller then realizes that an aircraft is just about to touch down on the runway. Controller states Tower view is blocked by Tower cab window pillars and they didn't see the aircraft because of the pillars.