PA-32 Cherokee Six/Lance/Saratoga/6X
Flight Crew Instrument
Flight Crew Last 90 Days 30; Flight Crew Total 330; Flight Crew Type 150
Human-Machine Interface; Situational Awareness; Distraction
Aircraft Equipment Problem Less Severe; Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter CFTT / CFIT
Flight Crew Returned To Clearance; Flight Crew Became Reoriented
Aircraft; Human Factors
While on initial approach RNAV 15 into IWS; approximately 1 mile outside of ORENT; I noticed I was below the glideslope. Minimum altitude at this point was 1700 msl and I was briefly as low as 1550 msl. This was discovered while scanning the instruments after reviewing the approach plate. Action was immediately taken to return to the proper altitude. I feel that a poorly lit altimeter contributed to this event as well as the distraction of a ringing cellphone.  Improved lighting of the altimeter as well as powering off any cell phones before critical phases of flight would have prevented this event.  The stress of making a night IFR approach into an unfamiliar field may also have contributed.
An IFR PA-32 pilot making a night time RNAV approach to IWS descended 150 FT below the FAF altitude when distracted by a ringing cellphone.  Also cited as contributing was poor lighting of the altimeter.