Caravan 208B
Flight Crew Air Transport Pilot (ATP)
Confusion; Situational Awareness; Workload
Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter CFTT / CFIT; Inflight Event / Encounter Unstabilized Approach
Air Traffic Control Issued Advisory / Alert; Flight Crew Became Reoriented; Flight Crew Returned To Clearance
Aircraft; Human Factors; Procedure
Arriving GSO being vectored for ILS 5R everything set up for 5R. While turning base for ILS 5R preceding Aircraft (AC) had a problem and was delaying on runway. ATC advised descend from 4;000 feet to 3;000 feet expect 5 Left localizer. I started descent to 3;000 and reset approach in radios to 5L. Rushed to change and set up approach. I was given a late turn to intercept and overshot localizer. That was followed by a turn to 080 to intercept maintain 3;000 till established clear for approach switch tower 119.1. I corrected back to intercept the localizer checked in with tower and was cleared to land. Intercepting the localizer I was now good to descend to 2;500 feet and was still above 3;000 feet descending. I mistook what I later identified as the VSI bug (that was about -450 fpm) as being slightly above glide slope and continued what I thought was slightly above glide slope descent. I broke out about the same time tower said we have a low altitude alert check your altitude. I stopped descent and could see I was lower than glide slope as field was further ahead. Tower asked me to confirm altitude 1;780 and I did. I then noticed green diamond bug had appeared I now realized that I had mistaken the glide slope indicator I maintained altitude at 1;780 joined real glide slope and landed.When they gave the late change to 5 Left I should have asked for a box around until I had everything set up primary and backup. My acceptance left me rushing to catch up leading to mistakes. when identified I was beneath the cloud deck on localizer below glide path 1;780 feet; joined glide path straight ahead and continued to landing.
A C208 pilot reports being assigned the ILS 5R at GSO initially then switched to ILS 5L due to an aircraft on the runway. The late change to 5L results in an overshoot of the localizer and an early descent due to mistaking the Vertical Speed Indicator (VSI) bug; at -450 FPM for the glideslope indicator. Tower then issues a low altitude alert at 1;800 feet and descent is stopped until the glideslope is captured from below.