B737-700 flight crew experienced difficulties attempting to practice a RNAV approach in VMC. Cws was...

Narrative:

On vectors with approach into jax; we requested the RNAV (GPS) 31. He asked if we could go direct nible (IAF); we accepted; and then started the turn. At this point we were past nible and had to turn about 140 degrees; virtually entering a downwind. Approach then cleared us for the RNAV approach. The captain was the pilot flying. I believe it was his first attempt at practicing an RNAV approach. I have only done one myself. Due to the close proximity to nible; the autopilot was turning right towards the fix and shortly started a left turn towards potme. At some point; the captain unknowingly disengaged LNAV and went into control wheel steering. I alerted him that he was in control wheel steering; but he did not respond. I'm not positive what happened next; but we were off course; confused with what the airplane was doing; and descending. The captain disengaged the autopilot and continued descending while flying away from the field. I instructed him a couple times to stop descending and that he needed to level off. I pointed in the direction of the field and told him we needed to climb and get back on glidepath. Due to being uncomfortable and fixated with the new RNAV procedures; the captain was unresponsive to my verbal alerts. As we started turning towards the field; we were off course and low. We had descended below the charted altitude at potme of 2;600 ft to about 1;700 ft MSL which is about nine miles from the TDZ. ATC alerted us to our altitude; I responded with 'correcting;' and requested the visual to 31. He cleared us for the visual. We got back on glidepath and landed. This event occurred as direct result of being unfamiliar with the new RNAV procedures. We; as pilots; must be extra aware and alert of our own limitations with these procedures. Always fly the airplane! I felt I was assertive as the pilot not flying; but there was room for improvement on my end as well. Listen to other crew members and always practice good CRM.

Original NASA ASRS Text

Title: B737-700 flight crew experienced difficulties attempting to practice a RNAV approach in VMC. CWS was inadvertently selected and the aircraft descended prematurely triggering a low altitude alert from ATC and an EGPWS warning. A visual approach ensued.

Narrative: On vectors with approach into JAX; we requested the RNAV (GPS) 31. He asked if we could go direct NIBLE (IAF); we accepted; and then started the turn. At this point we were past NIBLE and had to turn about 140 degrees; virtually entering a downwind. Approach then cleared us for the RNAV approach. The Captain was the pilot flying. I believe it was his first attempt at practicing an RNAV approach. I have only done one myself. Due to the close proximity to NIBLE; the autopilot was turning right towards the fix and shortly started a left turn towards POTME. At some point; the Captain unknowingly disengaged LNAV and went into Control Wheel Steering. I alerted him that he was in Control Wheel Steering; but he did not respond. I'm not positive what happened next; but we were off course; confused with what the airplane was doing; and descending. The Captain disengaged the autopilot and continued descending while flying away from the field. I instructed him a couple times to stop descending and that he needed to level off. I pointed in the direction of the field and told him we needed to climb and get back on glidepath. Due to being uncomfortable and fixated with the new RNAV procedures; the Captain was unresponsive to my verbal alerts. As we started turning towards the field; we were off course and low. We had descended below the charted altitude at POTME of 2;600 FT to about 1;700 FT MSL which is about nine miles from the TDZ. ATC alerted us to our altitude; I responded with 'correcting;' and requested the visual to 31. He cleared us for the visual. We got back on glidepath and landed. This event occurred as direct result of being unfamiliar with the new RNAV procedures. We; as pilots; must be extra aware and alert of our own limitations with these procedures. Always fly the airplane! I felt I was assertive as the pilot not flying; but there was room for improvement on my end as well. Listen to other crew members and always practice good CRM.

Data retrieved from NASA's ASRS site as of April 2012 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.

Attributes
ACN	885577
Time
Date	201004
Local Time Of Day	1201-1800
Place
Locale Reference	JAX.Airport
State Reference	FL
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	B737-700
Operating Under FAR Part	Part 121
Flight Phase	Initial Approach
Flight Plan	IFR
Person 1
Function	Pilot Not Flying First Officer
Experience	Flight Crew Last 90 Days 251
Person 2
Function	Pilot Flying Captain
Qualification	Flight Crew Air Transport Pilot (ATP)
Events
Anomaly	Deviation - Altitude Crossing Restriction Not Met Deviation - Altitude Excursion From Assigned Altitude Inflight Event / Encounter CFTT / CFIT

B737-700 flight crew experienced difficulties attempting to practice a RNAV approach in VMC. Cws was inadvertently selected and the aircraft descended prematurely triggering a low altitude alert from ATC and an egpws warning. A visual approach ensued.