Air carrier flight crew reported leaving cleared altitude earlier than ATC clearance allowed.

Attributes
ACN	1464906
Time
Date	201707
Local Time Of Day	1201-1800
Place
Locale Reference	TFFR.Airport
State Reference	FO
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	Large Transport
Operating Under FAR Part	Part 121
Flight Phase	Initial Approach
Flight Plan	IFR
Person 1
Function	First Officer Pilot Not Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Person 2
Function	Pilot Flying Captain
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Total 10000
Events
Anomaly	Deviation - Altitude Excursion From Assigned Altitude Deviation - Procedural Published Material / Policy Inflight Event / Encounter CFTT / CFIT

Narrative:

On approach into tffr we received clearance direct avset. Captain entered it manually and flew direct. We were then cleared to altitude 3600 and also cleared for the RNAV 12 approach. The aircraft leveled at 3600 feet until the flight mode annunciator displayed final app at which time the aircraft began to descend on its calculated profile which did not honor the altitude restriction at avset. ATC advised that we check our altitude and we climbed back up to 3600 and rearmed the approach.this event occurred due to the fact that when the avset direct was manually entered it did not include the restriction. The profile computed by the aircraft in final app was below this restriction. That fact that we were in VMC conditions possibly drew our attention to locating the field and reduced our verification process.insuring that when a direct is received that if it contains an altitude restrict that it is entered and to ensure that in final app that the aircraft respects all restrictions. Better balance of attention between inside and outside the aircraft.

Original NASA ASRS Text

Title: Air carrier flight crew reported leaving cleared altitude earlier than ATC clearance allowed.

Narrative: On approach into TFFR we received clearance direct AVSET. Captain entered it manually and flew direct. We were then cleared to altitude 3600 and also cleared for the RNAV 12 approach. The aircraft leveled at 3600 feet until the Flight Mode Annunciator displayed FINAL APP at which time the aircraft began to descend on its calculated profile which did not honor the altitude restriction at AVSET. ATC advised that we check our altitude and we climbed back up to 3600 and rearmed the approach.This event occurred due to the fact that when the AVSET direct was manually entered it did not include the restriction. The profile computed by the aircraft in FINAL APP was below this restriction. That fact that we were in VMC conditions possibly drew our attention to locating the field and reduced our verification process.Insuring that when a direct is received that if it contains an altitude restrict that it is entered and to ensure that in FINAL APP that the aircraft respects all restrictions. Better balance of attention between inside and outside the aircraft.

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.