Two mechanics report a Hawker 800 XP had declared an emergency landing due to low hydraulic pressure indication and landing gear slow to deploy after they performed troubleshooting maintenance for a wet nose gear strut.

Narrative

A Hawker 800XP was at our maintenance facility when hydraulic fluid was found on the nose gear during a postflight inspection by a flight crew member. A work order was issued by the aircraft's charter company to correct the discrepancy. I cleaned dried residual hydraulic fluid from the nosewheel steering actuator but after further investigation found no other hydraulic leaks present. The aircraft was pressurized by a hydraulic mule and the aircraft was jacked and gear swings were performed to troubleshoot for missing hydraulic fluid; but no further leaks were detected. A fellow AMT bled down the emergency brake/gear accumulators and I bled down the thrust reverser accumulators in the aft tail compartment of the aircraft. I inspected the hydraulic reservoir for any servicing requirements and; with my flashlight; looked at the hydraulic reservoir's sight tube and found it to be red and full of hydraulic fluid indicating that the reservoir was full and not needing any servicing. The aircraft was closed up and returned to service. It has come to my attention that the aircraft in question had departed and had declared an emergency landing due to a low hydraulic pressure indication and the landing gear slow to deploy. Upon further evaluation by the charter company's technicians; they had found that the hydraulic reservoir was 2 gallons low of hydraulic fluid. After hearing about this incident that I had been involved in; I feel that this aircraft has a possible undetected hydraulic leak and a bad discoloring of the hydraulic reservoir sight tube that may have led to a possible erroneous indication of the correct hydraulic quantity. Callback conversation with Reporter revealed the following information: Reporter ACN # 824726. Reporter stated the hydraulic quantity reservoir servicing is accomplished by filling the reservoir to one of three marks; noted on a fill plate. The marks allow for proper hydraulic fluid level if bleeding down the Emergency Brake/Gear accumulator; or thrust reverser accumulators separately; or both; or none at all. Reporter stated the Hawker hydraulic fluid is a red colored 5606 type.