Narrative:

While conducting the RNAV (GPS) LNAV approach to runway 08 at hyi; the descent was initiated from 2;400 feet MSL at kedce (final approach fix). The descent was continued down to 1;120 feet MSL which is the published minimum descent altitude for the approach until the missed approach point. The crew failed to note that the next minimum altitude was actually 1;620 feet MSL at nuhos which is located between the FAF and the map. The airplane broke out of the broken cloud layer at about 800 feet AGL and the captain (pilot not flying) called the runway in sight. The first officer (pilot flying) verbalized that it 'did not look right' and that the airplane seemed 'too low on the glide path' given the distance from the runway (about 3 miles). The captain agreed and; after again quickly glancing at the instrument approach procedure chart; realized the airplane was descended too early below the minimum altitude of 1;260 feet before nuhos. A climb was immediately initiated back up to the safe altitude.as the climb was initiated; the ground proximity warning system activated with an obstruction warning followed by a terrain warning. The obstacle warning was activated by the 859 foot tower published on the IAP chart near nuhos. At this time the airplane was still in visual meteorological conditions and visual contact with the runway; terrain; and obstructions was maintained until the airplane was climbed back up to a normal glide path with the runway. Visibility was good with 10 miles in light rain and the previously encountered cloud layer was nonexistent within 2 miles of the airport. The approach was continued normally and the airplane was landed safely. The local tower controller never mentioned any low altitude warning or anything else abnormal as the airplane cleared the runway and taxied to parking.crews should continue to be vigilant in adhering to minimum altitudes published for step-down fixes on non-precision instrument approaches. All fixes and their respective altitudes should be included in the approach briefing prior to initiating any kind of approach. I recommend that the classic 'dive and drive' style of descending on a non-precision approach should be avoided and a constant descent rate or angle should instead be computed and flown when lpv or VNAV is not available. This would help to ensure a safe descent path to the runway even if; in error; a minimum altitude at a fix is missed. Luckily in this case; the airplane broke out of the clouds and the crew realized it 'did not look right' visually before any GPWS activation. However; if the ceiling or visibility had been less; this could have become more of an issue especially in mountainous terrain. A human factor in this situation was complacency that can exist while operating in and out of an airport that is used regularly.

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Original NASA ASRS Text

Title: Air Taxi Captain reported descending below charted altitude on an RNAV approach to HYI airport when the crew failed to note an intermediate step-down altitude.

Narrative: While conducting the RNAV (GPS) LNAV Approach to Runway 08 at HYI; the descent was initiated from 2;400 feet MSL at KEDCE (Final Approach Fix). The descent was continued down to 1;120 feet MSL which is the published Minimum Descent Altitude for the approach until the Missed Approach Point. The crew failed to note that the next Minimum Altitude was actually 1;620 feet MSL at NUHOS which is located between the FAF and the MAP. The airplane broke out of the broken cloud layer at about 800 feet AGL and the Captain (Pilot Not Flying) called the runway in sight. The First Officer (Pilot Flying) verbalized that it 'did not look right' and that the airplane seemed 'too low on the glide path' given the distance from the runway (about 3 miles). The Captain agreed and; after again quickly glancing at the Instrument Approach Procedure chart; realized the airplane was descended too early below the Minimum Altitude of 1;260 feet before NUHOS. A climb was immediately initiated back up to the safe altitude.As the climb was initiated; the Ground Proximity Warning System activated with an obstruction warning followed by a terrain warning. The obstacle warning was activated by the 859 foot tower published on the IAP chart near NUHOS. At this time the airplane was still in Visual Meteorological Conditions and visual contact with the runway; terrain; and obstructions was maintained until the airplane was climbed back up to a normal glide path with the runway. Visibility was good with 10 miles in light rain and the previously encountered cloud layer was nonexistent within 2 miles of the airport. The approach was continued normally and the airplane was landed safely. The local Tower Controller never mentioned any low altitude warning or anything else abnormal as the airplane cleared the runway and taxied to parking.Crews should continue to be vigilant in adhering to minimum altitudes published for step-down fixes on non-precision instrument approaches. All fixes and their respective altitudes should be included in the approach briefing prior to initiating any kind of approach. I recommend that the classic 'dive and drive' style of descending on a non-precision approach should be avoided and a constant descent rate or angle should instead be computed and flown when LPV or VNAV is not available. This would help to ensure a safe descent path to the runway even if; in error; a minimum altitude at a fix is missed. Luckily in this case; the airplane broke out of the clouds and the crew realized it 'did not look right' visually before any GPWS activation. However; if the ceiling or visibility had been less; this could have become more of an issue especially in mountainous terrain. A human factor in this situation was complacency that can exist while operating in and out of an airport that is used regularly.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.