Date: 201712
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Daylight
Aircraft: HS 125 Series
Operator: Fractional
Operating under: Part 91
Mission: Test Flight / Demonstration
Flight phase: Initial Climb
Airspace: Class B ZZZ
ATC / advisory: Tower ZZZ
Aircraft component: Airspeed Indicator
Component problem: Malfunctioning
Reporter organization: Fractional
Reporter function: Captain; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Second reporter function: Pilot Flying; First Officer
Anomaly: Aircraft Equipment Problem Critical
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Returned To Departure Airport
Contributing factors: Aircraft; Procedure
Primary problem: Aircraft

Narrative: We (the Flight Crew) were assigned a post maintenance operational check flight in accordance with maintenance procedure. During the acceptance flow; a thorough log book review was accomplished by both the PIC and SIC. We did discover a previous [squawk] item for spurious WINDSHEAR as well as errors with attitude and airspeed mis-comparisons. The item was a discussion point since the corrective action did not appear to address the [squawk]; however; maintenance did accomplish maintenance actions and closed and corrected the [squawk]. During the subsequent takeoff; immediately after liftoff; we experienced WINDSHEAR aural and visual indications. Additionally; both left and right pilot altitude and airspeed data were mis-comparing. We decided that a return was prudent given the unknown status of indicating systems. During the remainder of the flight; neither left nor right altitude/airspeed information was reliable. Tower and Departure were notified of our status and ATC was informed that accurate information from the flight deck was questionable. The remainder of the flight was conducted without incident.Fortunately this issue occurred during an operational check flight with specific weather minimums. The erroneous altitude and airspeed information presented itself with as eerily similar to the Air Carrier Y accident scenario. Proactive detection; communication and utilization of external CRM (ATC) was incredibly important even in VMC conditions.


Second narrative: Just after breaking ground; we received both aural and annunciated windshear warnings along with amber IAS and ALT warnings on both PFDs. As we continued to climb out; the discrepancy between the Pilots and Copilots IAS and Altitude became greater; up to approximately 50 KIAS and more than 500 ft of altitude between the two PFDs. We in formed Departure that we needed to return and that we were having trouble with airspeed and altitude indications. We made a VFR pattern with an uneventful landing. Throughout the pattern; we were experiencing IAS and ALT warnings and we were not able to determine which side had the correct information. I elected to fly by reference to the AOA since the indicated speeds did not make sense with known power settings.


Synopsis: HS-125 flight crew reported a spurious windshear alert and erroneous airspeed and altitude indications immediately after takeoff on a post maintenance test flight.