Date: 201909
Local time of day: 1801-2400
Location: PAO.Airport, CA
Light: Daylight
Aircraft: Small Aircraft
Operating under: Part 91
Flight plan: VFR
Flight phase: Other VFR Traffic Pattern
Airspace: Class D PAO
ATC / advisory: Tower PAO
Second aircraft: Small Aircraft
Reporter organization: Government
Reporter function: Local
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Communication Breakdown; Situational Awareness
Anomaly: ATC Issue All Types; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued New Clearance
Contributing factors: Airspace Structure; Human Factors; Procedure
Primary problem: Airspace Structure

Narrative: Aircraft X was inbound from the North; North East to land at Palo Alto. They were a couple miles ahead of Aircraft Y who was handed off inbound from the North; who was over taking Aircraft X. Due to their relative positions and speed; the most operational advantages and safest route was for Aircraft X to enter a right base to Runway 31. I used automation to communicate the traffic request to Moffett Field (NUQ 1N). Moffett then called and say unable to Aircraft X. This resulted in me trying to communicate a very specific right base entry path for Aircraft X that would keep them clear of the NUQ Delta; which was not successfully done on my part. I had already sequenced Aircraft Y to follow Aircraft X; who had them in sight and was advised of the overtake. Aircraft X maneuvered towards mid field which resulted in them drifting to extremely close proximity to Aircraft Y who was on the mid field side of Aircraft X. After Aircraft Y reported the aircraft they were following didn't appear to be right base; I gave another instruction for Aircraft X to enter right base and then gave alternate following instruction to Aircraft Y to follow Aircraft X and remain inside the PAO Delta. I would note that Moffett did not appear to have any traffic at all during the time of the event. This type of congestion in the PAO airspace is complicated by airspace design where the busier airport (PAO) is routinely being denied airspace extensions requests and/ or transitions request skirting the NUQ airspace even when it would not affect their operations at all. The current airspace designs are decades old from when NUQ was still an active naval airbase and had a very different traffic operations than are routine for current Federal Air Field; which is restricted by the city of Sunnyvale in the number of operations it is authorized to have in a year. Palo Alto is now a significantly busier airport than Moffett and as most aircraft are sequenced into the VFR traffic pattern; routinely needs more airspace that is given by the current airspace design. The PAO should be redesigned to allow more room to sequence a VFR traffic pattern to a 3NM final with special consideration given to the NE quadrant to ensure any expanded airspace doesn't conflict with NUQ's departure corridor. I have made this suggestion for airspace redesign more than once. Permission to share a de-identified copy granted.




Synopsis: PAO Tower Controller reported an airspace deviation with an aircraft due to adjacent facility not allowing penetration for sequence.