PA28 ON ILS GAR CONFLICTS WITH TFC USING INTERSECTING RWY UNDER TWR CTL AT PHF.

Narrative

AFTER COMPLETING A VFR PRACTICE ILS APCH TO RWY 7; DURING THE MISSED APCH FROM OVER THE APCH LIGHTS AT 200+ FT AGL AND CLBING (I WAS THE SAFETY PLT); I OBSERVED A SINGLE ENG HIGH WING CESSNA TO OUR L OVER RWY 20. WE WERE CLRED FOR THE OPTION RWY 7 FROM A 3 MI FINAL. THESE RWYS CROSS NEAR THE APCH END OF RWY 7 AND DEP END OF RWY 20. SINCE THIS CESSNA WAS ABOUT 1/4 MI TO MY L AND AT APPROX THE SAME ALT; I TOOK CTL OF THE ACFT FROM THE PLT UNDER THE HOOD; REDUCED PWR AND LOWERED THE NOSE TO ENSURE WE WOULD PASS WELL CLR BENEATH THE CLBING CESSNA. I BELIEVE THE CESSNA PASSED ABOVE AND BEHIND US. APPARENTLY; THE LCL CTLR AT THE TWR DID NOT ENSURE THE CESSNA WOULD CROSS THE RWY 20 THRESHOLD AFTER WE PASSED THE INTXN OF THE 2 RWYS. IF THE CESSNA WAS CLRED FOR THE LOW APCH; OR THE CTLR CLRED THE CESSNA FOR TKOF OR TOUCH-AND-GO BEFORE WE PASSED THE INTXN; THIS WAS AN ERROR OF JUDGEMENT IN ANTICIPATING INTERSECTING RWY SEPARATION AFTER ISSUING CLRNCS. LCL CTLR FAILED TO ENSURE INTERSECTING RWY SEPARATION FOR 2 ACFT; EACH USING DIFFERENT RWYS AT THE SAME AERODROME. CTLRS NEED TO EXERCISE GREATER VIGILANCE TO ENSURE RWY SEPARATION; WHEN TFC CONDITIONS INCREASE IN VOLUME AND COMPLEXITY.