Narrative:

Aircraft descended to 580 ft MSL; 80 ft below MDA (660 ft MSL) while on the final approach segment of the RNAV 23 (circle 32). How the problem arose:- weather 50 ft above minimums; in flight visibility 1 1/2 miles in rain.- pilot not flying: instructor pilot (front cockpit)- pilot flying: pilot under instruction (rear cockpit)- first instructional instrument flight with a transition pilot new to the texii- transition pilot's first exposure to RNAV runway 23 approach- while transition pilot had briefed MDA of 660 ft MSL; during the execution of the approach; he 'had it in his head' that the MDA was 600 ft MSL- as aircraft approached MDA at approximately 3.0 NM from threshold of runway 23; the tower stated 'report cancelling IFR'; at which point I shifted my scan outside; attempting to locate the runway environment/see if we could 'cancel IFR'.- while looking outside; I was unable to see anything; due to heavy rain on the windscreen.- while looking outside; north whiting tower called 'check altitude'.- after hearing tower's admonition; I shift my scan back inside; noting 580 ft MSL and directing a climb to 660 ft MSL; at which point the pilot flying applied power and began a climb.- shortly thereafter; at 1 1/2 miles; the field came into view and we executed an uneventful circle to land maneuver.contributing factors:- my decision to allow the pilot under instruction to fly the approach to the MDA with weather near minimums.- belief of the pilot under instruction that the MDA was 600 ft MSL vice 660 ft MSL.- my scan being outside prior to ensuring the level off at MDA.- the radar altimeter was not set to an altitude useful to alert our crew to a descent below MDA.corrective actions:- deviation was debriefed following the event.- as the instructor pilot; I have changed my personal 'rules of engagement' when allowing a student to shoot the approach - specifically that until I see the student established at MDA; I will not shift my scan outside.- ensuring the student sets the MDA in the altitude bug; to assist in leveling off at the actual MDA.- ensure the radar altimeter is set at 10% below the high above touchdown in order to provide an alert in the case of another inadvertent descent below MDA.

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Original NASA ASRS Text

Title: The instructor pilot in Beech Texan II was distracted looking for the airport as the student failed to arrest their descent at the MDA. ATC issued an altitude alert and they recovered back to the MDA.

Narrative: Aircraft descended to 580 FT MSL; 80 FT below MDA (660 FT MSL) while on the final approach segment of the RNAV 23 (Circle 32). How the problem arose:- Weather 50 FT above minimums; in flight visibility 1 1/2 miles in rain.- Pilot not flying: Instructor pilot (front cockpit)- Pilot flying: Pilot under instruction (rear cockpit)- First instructional instrument flight with a transition pilot new to the TEXII- Transition pilot's first exposure to RNAV Runway 23 approach- While transition pilot had briefed MDA of 660 FT MSL; during the execution of the approach; he 'had it in his head' that the MDA was 600 FT MSL- As aircraft approached MDA at approximately 3.0 NM from threshold of Runway 23; the Tower stated 'report cancelling IFR'; at which point I shifted my scan outside; attempting to locate the runway environment/see if we could 'cancel IFR'.- While looking outside; I was unable to see anything; due to heavy rain on the windscreen.- While looking outside; North Whiting Tower called 'check altitude'.- After hearing Tower's admonition; I shift my scan back inside; noting 580 FT MSL and directing a climb to 660 FT MSL; at which point the pilot flying applied power and began a climb.- Shortly thereafter; at 1 1/2 miles; the field came into view and we executed an uneventful circle to land maneuver.Contributing factors:- My decision to allow the pilot under instruction to fly the approach to the MDA with weather near minimums.- Belief of the pilot under instruction that the MDA was 600 FT MSL vice 660 FT MSL.- My scan being outside prior to ensuring the level off at MDA.- The RADAR altimeter was not set to an altitude useful to alert our crew to a descent below MDA.Corrective actions:- Deviation was debriefed following the event.- As the instructor pilot; I have changed my personal 'rules of engagement' when allowing a student to shoot the approach - specifically that until I see the student established at MDA; I will not shift my scan outside.- Ensuring the student sets the MDA in the altitude bug; to assist in leveling off at the actual MDA.- Ensure the radar altimeter is set at 10% below the High Above Touchdown in order to provide an alert in the case of another inadvertent descent below MDA.

Data retrieved from NASA's ASRS site as of July 2013 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.