H25B HAD A RWY INCURSION ON RWY 4 AT HOU; IN THE RAIN; AND REDUCED VISIBILITY.

Narrative

H25B ACFT; 2 CREW MEMBERS ABOARD AS REQUIRED; OPERATING ON AN IFR FLT PLAN; WAS GIVEN CLRNC TO TAXI FROM RAMP AREA AND EXECUTE A R TURN ONTO THE TXWY WITH CLRNC TO RWY 4. VISIBILITY WAS GREATLY REDUCED BY INTERMITTENT RAIN SHOWERS. THE R SEAT PLT WAS REFING THE ARPT DIAGRAM AND PROMPTING THE L SEAT PLT. THE TXWY WAS WET; THE VISIBILITY MARGINAL; WHICH PROMPTED THE L SEAT PLT WHO WAS TAXIING THE ACFT TO ASK HOW FAR DOWN THE TXWY DO WE GO. THE R SEAT PLT RESPONDED BY SAYING 'ALL THE WAY DOWN.' THE ACFT WAS TAXIED A SHORT DISTANCE WHEN THE L AND R SEAT PLTS BOTH REALIZED THE ACFT HAD CROSSED OVER THE HOLD SHORT LINE FOR RWY 4. THE LINE WAS ESTIMATED TO BE JUST UNDER THE TAIL. THE EVENT WAS OBSERVED BY THE TWR AND THE ACFT WAS GIVEN CLRNC TO TAXI INTO POS ON RWY 4 AND HOLD. AFTER TKOF; A FOLLOW-UP CALL WAS MADE TO THE TWR AND A BRIEF DISCUSSION REGARDING THE MATTER TOOK PLACE. THE FOLLOW-UP CALL CLOSED THE ISSUE ON A POSITIVE NOTE. RWY INCURSIONS ARE A MAJOR ISSUE. COCKPIT VIGILANCE HAS GOT TO BE A FIRST PRIORITY. TAXI CLRNCS MUST BE EXECUTED CORRECTLY. ONE PLT MUST DOUBLECHK THE TAXI RTE ON THE ARPT DIAGRAM AND MONITOR ACFT POS AND PROMPT THE PLT TAXIING THE ACFT. COCKPIT CREW MEMBERS MUST BE VIGILANT AT ALL TIMES. STRICT VIGILANCE MUST BE MAINTAINED WHILE OTHER COCKPIT DUTIES ARE BEING ACCOMPLISHED. IN THIS INSTANCE AS DESCRIBED; BETTER COM BTWN THE 2 PLTS AND A HEIGHTENED AWARENESS OF ACFT POS WOULD HAVE AVOIDED THE EVENT EVER TAKING PLACE.