B737 first officer reported receiving a low altitude alert from ATC while on an rnp approach after e...

Attributes
ACN	1717204
Time
Date	202001
Local Time Of Day	1201-1800
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	B737 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	Descent
Route In Use	Other RNP
Flight Plan	IFR
Person 1
Function	First Officer
Qualification	Flight Crew Air Transport Pilot (ATP) Flight Crew Instrument Flight Crew Multiengine
Events
Anomaly	Deviation - Altitude Excursion From Assigned Altitude Deviation - Procedural Clearance Deviation - Procedural Published Material / Policy Inflight Event / Encounter CFTT / CFIT

Narrative:

I was the pilot flying on the leg into ZZZ. We were set up for the rnp M runway xx. I made 2;000 at zzzzz a hard altitude instead of an at or above to make sure I wasn't high on my arrival. After being cleared for the rnp M to runway xx in ZZZ; I was in LNAV and VNAV and in the path so I set field elevation. Prior to reaching the XXX fix; we were told by ZZZ center of a low alt alert. We were at 4;200 and the min alt prior to XXX fix is 5;000. We were in VMC with all terrain in sight. We climbed back up to 5;000 and continued with the approach and landed uneventfully on xx. Somehow the 5;000 restriction got removed from the XXX waypoint in the legs page of the FMC; so we descended through it while established on the VNAV path.pilots need to be careful to check all altitudes on the legs page to prevent this from occurring.

Original NASA ASRS Text

Title: B737 First Officer reported receiving a low altitude alert from ATC while on an RNP approach after entering the airport elevation in the FMC; which may have removed an altitude restriction.

Narrative: I was the pilot flying on the leg into ZZZ. We were set up for the RNP M RWY XX. I made 2;000 at ZZZZZ a hard altitude instead of an at or above to make sure I wasn't high on my arrival. After being cleared for the RNP M to Runway XX in ZZZ; I was in LNAV and VNAV and in the path so I set field elevation. Prior to reaching the XXX fix; we were told by ZZZ Center of a low alt alert. We were at 4;200 and the min alt prior to XXX fix is 5;000. We were in VMC with all terrain in sight. We climbed back up to 5;000 and continued with the approach and landed uneventfully on XX. Somehow the 5;000 restriction got removed from the XXX waypoint in the legs page of the FMC; so we descended through it while established on the VNAV path.Pilots need to be careful to check all altitudes on the legs page to prevent this from occurring.

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.

B737 first officer reported receiving a low altitude alert from ATC while on an rnp approach after entering the airport elevation in the FMC; which may have removed an altitude restriction.