Medium Transport; Low Wing; 2 Turbojet Eng
Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 3
Troubleshooting; Situational Awareness; Communication Breakdown; Distraction
Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Landing Without Clearance; Ground Incursion Runway
Environment - Non Weather Related; Human Factors; Procedure
I was working Local control and Ground control combined.  We had just combined the positions roughly 15 minutes prior to me taking the positions.  I had approximately 3 aircraft taxiing; two aircraft waiting to depart at the runways; one aircraft on his take off roll; and two aircraft inbound on visual approaches.  One aircraft was inbound for Runway 10L (Aircraft X) and one inbound 5 miles in trail of the first aircraft inbound for 10R.  The aircraft on his take off roll on 10R reported about 20 geese in the grass south of the approach end of the runway.  I was able to get in contact with an airport ops vehicle who was able to get to the runway to try to get the geese to fly off.  There was a lot of frequency congestion but it wasn't unmanageable.  The second aircraft inbound for 10R checked on and was told to continue due to a vehicle on the runway trying to remove geese.  About 20 seconds later I asked the aircraft inbound for 10R if he would like to change to runway 10L as a precaution for the geese; and he agreed.  I cleared him for 10L and airport ops was free to continue the removal of the birds.  Aircraft X rolls out on 10L and the aircraft that changed runways to 10L was now on about a 4 mile final.  I transmitted to Aircraft X to exit the runway at E2 and taxi to the ramp; but there was no answer.  I again transmitted to Aircraft X to exit at E2 and taxi to the ramp; and again no answer.  Aircraft X exited the runway at E2 and cleared the runway but stopped on the taxi way.  After about 10 seconds or so Aircraft X transmits to me and I taxi him into the ramp.  Once Aircraft X gets to the ramp he advises me he doesn't believe he received a landing clearance.  I advised the pilot that I thought I had given him a clearance and was talking to him and aware of him the whole time; he advised that he thought he received a clearance and was on my frequency the whole time as well but after thinking about it he wasn't sure whether he received one or not.  There was no loss of separation or runway incursion as a result of the communication error.  The next day I listened to the tapes and was able to determine that Aircraft X never checked on with me on the Local frequency and never received a landing clearance.  I was distracted with the bird removal; changing another aircraft to a different landing runway; and other traffic taxiing and I assumed I had already given him the clearance which was not the case.  I also listened to North Radar to see if he was ever issued a switch from radar.  Radar never switched Aircraft X to my frequency; however when Aircraft X was established on final he transmitted to North Radar 'Verify Aircraft X is cleared to land on 10L'.  When he transmitted this to radar; another aircraft transmitted at the same time blocking the transmissions.  Radar had the aircraft say again; and again both aircraft transmitted and radar was able to answer the other aircraft but wasn't able to understand or answer Aircraft X.  Aircraft X doesn't try again to get a verification of his clearance nor does he question being on the wrong frequency.This whole situation was really attributed I think to a series of unforeseen circumstances that made an otherwise busy but routine traffic session more complex and led to a breakdown of communication.  It is standard practice to combine ground and local control around XA:00 and XA:30 because that is usually when traffic starts to slow for the evening.  The geese along with the vehicle needing to be on the runway to clear the geese and the aircraft on final changing runways for precaution added complexity to the situation.  I think there was complacency on the part of the pilot since he never received his clearance; and questions it on the frequency yet never receives his verification of clearance; and no longer tries to receive his verification. After not receiving his verification he lands anyway; so I would recommend that first if a pilot has any question at all a bout a clearance he needs to get a clear and concise verification.  Also if he doesn't receive the verification or is told to say again he should be adamant about verifying his clearance and not stop trying until he gets it.   I would also recommend on the part of the local controller; if I have any question whatsoever about a landing clearance I should just transmit in the blind and re issue the clearance and that will tell me whether or not the aircraft is on my frequency or not; even if the situation is safe and theres no chance of a loss of separation or incursion as this event was.  Third I would recommend that as a radar controller; he should have tried a little harder to answer the second unanswered aircraft.  I understand if he says say again and the pilot doesn't answer then usually we just move on to the next transmission; but maybe he should have tried one or two more times to get in contact with the unanswered aircraft.
CMH Tower Controller reports of a distraction to the scenario with a gaggle of geese in close proximity to an active runway.  Controller never issues landing clearance to an aircraft.