Air carrier flight crew reported descending below the mia runway 26R RNAV approach profile. The auto...

Attributes
ACN	1477252
Time
Date	201708
Local Time Of Day	1201-1800
Place
Locale Reference	MIA.Airport
State Reference	FL
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	Widebody Transport
Operating Under FAR Part	Part 121
Flight Phase	Final Approach
Route In Use	Other RNAV (GPS) Runway 26R
Flight Plan	IFR
Component
Aircraft Component	Autoflight System
Person 1
Function	Captain Pilot Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Person 2
Function	Pilot Not Flying First Officer
Qualification	Flight Crew Air Transport Pilot (ATP)
Events
Anomaly	Deviation - Altitude Excursion From Assigned Altitude Inflight Event / Encounter CFTT / CFIT Inflight Event / Encounter Weather / Turbulence

Narrative:

Uneventful descent into miami while avoiding thunderstorms. Vectors to intercept final course for RNAV/GPS rwy 26R. We kept the speed up to get on the ground before a series of thunderstorms got to the airport and received shortened vectors to final inside the nayib fix on the approach. On final and after confirming FMS speed; nav; and profile MDA; while consulting with each other about rain showers close to the airport; we noticed that the airplane was descending below the profile glidepath and I disconnected the autopilot to arrest the descent. We descended to 1300; below the minimum 1500 ft for that portion of the approach before the final approach fix zarer. We immediately started a correction back to published altitude. At that point we received a yellow ground proximity alert for several buildings 2 to 3 miles in front and on both sides of the approach course. After confirming we were well clear of all obstacles and still in a safe position for landing we opted to visually continue the approach and landing. Distraction with weather during the approach. Clarify before the approach the duties (i.e. Who will be looking at the radar and who will be closely monitoring the instruments).

Original NASA ASRS Text

Title: Air carrier flight crew reported descending below the MIA Runway 26R RNAV Approach profile. The autopilot did not capture the vertical path and the crew did not detect it until they were low causing a GPWS warning.

Narrative: Uneventful descent into Miami while avoiding thunderstorms. Vectors to intercept final course for RNAV/GPS Rwy 26R. We kept the speed up to get on the ground before a series of thunderstorms got to the airport and received shortened vectors to final inside the NAYIB fix on the approach. On final and after confirming FMS speed; Nav; and profile MDA; while consulting with each other about rain showers close to the airport; we noticed that the airplane was descending below the profile glidepath and I disconnected the Autopilot to arrest the descent. We descended to 1300; below the minimum 1500 ft for that portion of the approach before the Final Approach Fix ZARER. We immediately started a correction back to published altitude. At that point we received a yellow GROUND PROXIMITY alert for several buildings 2 to 3 miles in front and on both sides of the approach course. After confirming we were well clear of all obstacles and still in a safe position for landing we opted to visually continue the approach and landing. Distraction with weather during the approach. Clarify before the approach the duties (i.e. who will be looking at the radar and who will be closely monitoring the instruments).

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.

Air carrier flight crew reported descending below the mia runway 26R RNAV approach profile. The autopilot did not capture the vertical path and the crew did not detect it until they were low causing a GPWS warning.