Narrative:

On initial approach to sequ; RNAV (rnp) runway 35; between dagma and anbur a descent below the anbur restriction of 14;820 ft occurred to approximately 13;900 ft. An immediate correction and return to 14;800 ft was initiated. No terrain cautions or warnings occurred. A major contributer at the time of the incident was VNAV path had changed to VNAV speed; and was not immediately noticed. The FAF altitude of 11;500 ft that was set in the MCP was not reset to 14;900 ft for anbur when in VNAV speed. Strict adherence to all company procedures for sequ would have most likely prevented this unfortunate event. I think the first officer's mental alertness (tired) could have played a part; although when asked he denied it.

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Original NASA ASRS Text

Title: B757 Flight Crew reports descending below 14;820 FT prior to ANBUR during the RNAV Runway 35 approach to SEQU. VNAV had become disengaged without the crew noticing.

Narrative: On initial approach to SEQU; RNAV (RNP) Runway 35; between DAGMA and ANBUR a descent below the ANBUR restriction of 14;820 FT occurred to approximately 13;900 FT. An immediate correction and return to 14;800 FT was initiated. No terrain cautions or warnings occurred. A major contributer at the time of the incident was VNAV PATH had changed to VNAV SPD; and was not immediately noticed. The FAF altitude of 11;500 FT that was set in the MCP was not reset to 14;900 FT for ANBUR when in VNAV SPD. Strict adherence to all company procedures for SEQU would have most likely prevented this unfortunate event. I think the First Officer's mental alertness (tired) could have played a part; although when asked he denied it.

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.