While one controller was relieving another controller on position; a ground vehicle towing an aircra...

Narrative:

I was just taking the briefing for the start of my overtime mid-shift on all positions in the tower. I was briefed on runway 26L in use; west flow will be going to contra on the upcoming ATIS; aircraft X taxiing to runway 26L; aircraft on final taken and not talking to; and then gave initials. The initials appeared to not be relayed on the tapes; the briefing button may have been simultaneously pressed when we gave our initials. As I was looking up from the briefing and starting a new scan I noticed a light from taxiway hotel and at the same time aircraft Y called the tower on tower/ground frequency; 'ontario tower; aircraft Y.' at this same time I saw aircraft X passing taxiway hotel on taxiway november. By being familiar with the midshift and the repositioning of aircraft Y during this time of night I deduced that this aircraft was requesting to continue his reposition. I transmitted 'aircraft Y; ontario tower reposition approved via november-papa; thank you.' four hours later I was notified that aircraft Y called and said that he had to slam on the brakes to avoid going onto taxiway november and avoid hitting or being hit by aircraft X. I reviewed the tapes and aircraft Y was never given a hold short instruction or given traffic on taxiway november. Aircraft X was also not given any hold short instruction or notified of traffic taxiing out of taxiway hotel onto november. I was never briefed of aircraft Y being authorized to reposition/tow from taxiway hotel to the gate.I would have recommended either the previous controller have given aircraft Y a hold short instruction (hold short of taxiway november) or have had them give a notification after the push and when they were to begin the reposition process to serve as a reminder. A note of the reposition would have also helped to serve as a memory aid during the briefing.

Original NASA ASRS Text

Title: While one Controller was relieving another Controller on position; a ground vehicle towing an aircraft had to brake suddenly to avoid a taxiing aircraft.

Narrative: I was just taking the briefing for the start of my overtime mid-shift on all positions in the tower. I was briefed on RWY 26L in use; WEST FLOW will be going to Contra on the upcoming ATIS; Aircraft X taxiing to Runway 26L; aircraft on final taken and not talking to; and then gave initials. The initials appeared to not be relayed on the tapes; the briefing button may have been simultaneously pressed when we gave our initials. As I was looking up from the briefing and starting a new scan I noticed a light from Taxiway Hotel and at the same time Aircraft Y called the tower on tower/ground frequency; 'Ontario Tower; Aircraft Y.' At this same time I saw Aircraft X passing Taxiway Hotel on Taxiway November. By being familiar with the midshift and the repositioning of Aircraft Y during this time of night I deduced that this aircraft was requesting to continue his reposition. I transmitted 'Aircraft Y; Ontario Tower reposition approved via November-Papa; thank you.' Four hours later I was notified that Aircraft Y called and said that he had to slam on the brakes to avoid going onto Taxiway November and avoid hitting or being hit by Aircraft X. I reviewed the tapes and Aircraft Y was never given a hold short instruction or given traffic on Taxiway November. Aircraft X was also not given any hold short instruction or notified of traffic taxiing out of Taxiway Hotel onto November. I was never briefed of Aircraft Y being authorized to reposition/tow from Taxiway Hotel to the gate.I would have recommended either the previous controller have given Aircraft Y a hold short instruction (hold short of Taxiway November) or have had them give a notification after the push and when they were to begin the reposition process to serve as a reminder. A note of the reposition would have also helped to serve as a memory aid during the briefing.

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.

Attributes
ACN	1370110
Time
Date	201607
Local Time Of Day	1801-2400
Place
Locale Reference	ONT.Tower
State Reference	CA
Environment
Light	Night
Aircraft 1
Make Model Name	Widebody Low Wing 2 Turbojet Eng
Operating Under FAR Part	Part 121
Flight Phase	Taxi
Route In Use	None
Flight Plan	IFR
Aircraft 2
Make Model Name	Large Transport Low Wing 2 Turbojet Eng
Flight Phase	Taxi
Route In Use	None
Person 1
Function	Local Supervisor / CIC Ground
Qualification	Air Traffic Control Fully Certified
Experience	Air Traffic Control Time Certified In Pos 1 (yrs) 0.5
Person 2
Function	Local Ground Supervisor / CIC
Qualification	Air Traffic Control Fully Certified
Experience	Air Traffic Control Time Certified In Pos 1 (yrs) 7
Events
Anomaly	ATC Issue All Types Conflict Ground Conflict Critical

While one controller was relieving another controller on position; a ground vehicle towing an aircraft had to brake suddenly to avoid a taxiing aircraft.