Date: 201211
Local time of day: 0001-0600
Location: GLS.Airport, TX
Flight conditions: VMC
Weather elements / visibility: 10
Light: Night
Aircraft: S-76/S-76 Mark II
Operator: Air Taxi
Operating under: Part 135
Flight plan: None
Mission: Training
Flight phase: Final Approach
Airspace: Class G GLS
ATC / advisory: CTAF GLS
Second aircraft: Small Aircraft; Low Wing; 2 Eng; Retractable Gear
Reporter organization: Air Taxi
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Multiengine; Flight Crew Flight Instructor; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Human factors: Other / Unknown
Anomaly: Conflict NMAC; Deviation / Discrepancy - Procedural FAR; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Automation Aircraft TA; Person Flight Crew
When detected: In-flight
Result: General None Reported / Taken
Contributing factors: Human Factors
Primary problem: Human Factors

Narrative: During a routine Part 91 Ops flight check; I departed Runway 35 at GLS and remained in left closed traffic; making all advisory calls on the CTAF frequency. This event was occurring prior to the Tower resuming Class D operations at 0600. While on the downwind leg; my First Officer and I noticed some lights in the distance at a very low altitude of the water in the GOM [Gulf of Mexico]; it appeared as lights on one of the off-shore platforms. We continued on downwind; base; to final making all advisory calls; there was no other traffic in the vicinity; and no other advisory calls were being made. On short final to Runway 35 and the intersection of Taxiway Delta; at about 50 FT AGL; just prior to touchdown; a multi-engine fixed-wing aircraft appeared from underneath our aircraft rolling down Runway 35 to exit at Taxiway Echo to taxi into the General Aviation ramp. At the time this was occurring; my TCAS went off; I proceeded to land on Runway 35 at Taxiway Delta well clear of the fixed-wing aircraft that was now taxiing off the runway at Echo. After landing and parking; I proceeded over to the other aircraft and pilots to address the incident with them. The Captain advised that he observed us from a distance; but wasn't sure if we were a fixed-wing or helicopter; as he got closer he realized it was a helicopter and decided to go ahead and land on the runway behind and below us as we were landing. He said he was in a hurry due to a patient transport and didn't want to do a go-around. This pilot is a Mexican national flying a Mexican registered aircraft. He was flying so low over the water that he lost communication with Houston Center; never communicated with Approach Control; and was monitoring the GLS UNICOM frequency; and not the proper CTAF frequency; thus; not hearing our position reports; and never knowing he was even there until he appeared from underneath our aircraft at 50 FT AGL. Had we shot our approach to Taxiway Charlie; not Delta; this would have been disastrous; and there would be four dead individuals; and two destroyed aircraft.




Synopsis: Helicopter pilot reports NMAC with a light twin during landing at GLS.  The light twin pilot reportedly was not using the CTAF and saw the helicopter ahead and elected to expedite his approach and land under the helicopter.