Date: 201707
Local time of day: 1801-2400
Location: JNU.Airport, AK
Light: Daylight
Aircraft: Beaver DHC-2
Operating under: Part 91
Flight phase: Taxi
ATC / advisory: Tower JNU
Second aircraft: Cessna Aircraft Undifferentiated or Other Model
Reporter organization: Government
Reporter function: Local
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Situational Awareness; Distraction; Confusion
Second reporter function: Single Pilot; Pilot Flying
Anomaly: ATC Issue All Types; Conflict NMAC; Deviation / Discrepancy - Procedural Published Material / Policy; Ground Incursion Runway
Detector: Person Flight Crew
When detected: Taxi
Contributing factors: Airport; Procedure; Human Factors; Aircraft
Primary problem: Procedure

Narrative: Now; there was no loss of separation; but there were a handful of things that happened that were kind of bad. So; Aircraft Y called up; ready to go. I scanned the lane and cleared them for takeoff. Seconds after this; Aircraft X called up; stated they were west of the aircraft taking off and needed to cross. Now; when I scanned; I only saw one aircraft moving on the pond; Aircraft Z; so when I saw Aircraft X in relation to this aircraft; it was cool and crossing was no big deal. I crossed Aircraft X and noted that Aircraft Y was taking an awful long time to start takeoff roll. A second or two later; something caught my eye to the west and I saw Aircraft Z in the water lane. I; quickly as I could; instructed Aircraft X to hold short and kept him from entering the water lane. Aircraft Y then departed without incident.When Aircraft X departed I told them to let me (the controller) determine who they were west and east; they said they hadn't seen Aircraft Z behind them.It all worked out; but it could have been way worse.Better scans; I figured out that Aircraft Z; I hadn't seen was behind one of the window beams.


Second narrative: I was leaving my float plane dock at the JNU airport for a flight seeing trip with 2 others on board. The float pond is an active runway; so I called the tower with my numbers; position; direction of flight and the ATIS; requesting a crossover N to S at the end. Didn't hear a response right away; and was getting ready to call again when I hear crossover approved; with no N number. Thought that strange; probably a new person in the tower; stated I was crossing and started. Next thing I see is an aircraft that had taken off behind me and was airborne flying in front of us; and the tower is asking me to identify and what are you doing? There was a second plane behind me; and they had given him clearance to cross after the departing plane had passed; not me. It appears my transmissions were blocked by others talking on the radio and I was unaware the tower had never heard me; as I also had not heard other transmissions as I was talking. Corrective action; I will never move under a tower command until I hear my N number repeated to me; and the tower should never authorize movement without stating an N number first; which I believe happened; them thinking only one plane was on the pond ready to move. Have to realize just because one makes a radio transmission does not mean the other party heard it; so need to make sure any communication heard is actually directed to me and not some other plane.


Synopsis: Juneau Tower Controller and departing pilot reported confusion on who was to depart resulting in what the pilot reported as a NMAC.