Air carrier Captain reported GPS jamming departing OJAQ/AQB. Normal GPS operations were resumed after departing the area.

Narrative

GPS Jamming / SpoofingAQJPre-departure and DepartureLoss of GPS PRIMARY; reversion to IRS (Inertial Reference System) and radio navDuring the initial cockpit setup; a significant discrepancy was observed between the ADIRS (Air Data Inertial Reference System)-aligned position and the surveyed stand coordinates. Multiple attempts to realign the IRS yielded the same inaccurate results; indicating possible GPS spoofing or jamming.To isolate the issue; a reset of the Multi-Mode Receiver (MMR) was performed by maintenance personnel to rule out internal receiver faults. Following the reset; GPS functionality appeared nominal; but it was confirmed that GPS PRIMARY would remain unavailable due to external jamming/spoofing at the location.IRS alignment was completed using radio navigation updating in lieu of GPS.The RNP 1 departure was rejected due to inability to assure required navigation accuracy.An alternative conventional departure procedure was coordinated with ATC and executed using hard-tuned VOR/DME raw data (bearing and distance) and positioning.To prevent navigation degradation from fluctuating or false GPS inputs; the GPS position inputs were manually deselected via the MCDU (Multi-purpose Control Display Unit) prior to departure.During departure and climb through the GPS-denied area; a map shift was observed; as expected and briefed; due to IRS drift in the absence of GPS updating.Once clear of the jamming zone; GPS inputs were re-enabled; and GPS PRIMARY was recovered with NAV ACCURACY: HIGH confirmed on the MCDU.A comprehensive threat assessment and crew briefing was conducted prior to departure; in accordance with SOPs. Specific mitigation strategies included:Use of raw VOR/DME data to validate position and maintain situational awarenessBriefing on expected map shift and possible degraded navigation performanceATC notified of the need for procedural adjustments for departure This event highlights the operational impact of GPS jamming/spoofing; particularly on PBN (Performance Based Navigation) procedures such as RNP departures. The ability to recognize unreliable position data; isolate GPS inputs; and revert to alternate nav sources is critical.Emphasize GPS denial procedures and manual nav source selection during training; and ensure crews are familiar with the limitations of FMS navigation in degraded environments.