UA.V.C.K4: Loss of Global Positioning System (GPS) signal during flight and potential consequences.

ACS Area V — Operations Task C: Emergency Procedures References: AC 107-2; FAA-H-8083-25; FAA-G-8082-22; SAFOs 09013, 10017, 15010

Key Concepts

Recognizing GPS Loss and Its Immediate Effects

A loss or degradation of navigation signal is typically indicated by a “flag”—a warning device on navigation instruments that shows the instrument is inoperative or that the received signal’s strength/quality is below acceptable values. Treat any GPS “flag” or equivalent alert as a loss of reliable position data, and be prepared for automation modes (position hold, route following) to degrade or disconnect.^[6]
Some navigation systems continuously update position accuracy by referencing multiple conventional navigation aids through a Flight Management System (FMS). The FMS uses a large database and automatically selects the most appropriate aids during its update cycle. If GPS becomes unavailable and no other aids are available to the system, expect navigation accuracy to degrade and automation to rely on less precise sources or revert to basic modes.^[2]

Preflight Planning and Contingency Actions (Emergency Procedures under §107.49)

Before flight, the remote PIC must complete preflight familiarization, inspection, and actions, including planning for emergency procedures and applying sound risk management and aeronautical decision-making. These actions are required prior to beginning operations (§ 107.49). Loss of GPS is a foreseeable contingency that should be briefed and practiced.^[3]
The preflight assessment must address at least: local weather conditions; local airspace and any flight restrictions; the location of persons and moving vehicles not directly participating; whether the operation will be conducted over an open-air assembly; the potential for nonparticipants or vehicles to enter the area; and other ground hazards. If GPS is lost, these factors determine where you can safely maneuver or terminate the flight without relying on satellite navigation.^[3]
Be aware of the type of airspace in which you will operate. Using a current aeronautical chart or tools like the B4UFLY app supports decision-making about airspace and restrictions—critical if you must navigate visually after a GPS outage.^[3]

Maintaining Control and Navigating Without GPS

Your primary task is to maintain the intended flight path when automation falters. A flight path is the line, course, or track along which an aircraft is flown or intended to be flown. If GPS-supported modes disengage, transition to manual control to keep the aircraft on a safe path you have preplanned.^[2]
Without GPS, determine position using visual references. A fix is a geographical position determined by visual reference to the surface, by reference to radio NAVAIDs, by celestial plotting, or by another navigational device. For sUAS, this practically means orienting to distinct surface features (landmarks) you identified during preflight so you can navigate back or to a predetermined safe area without satellite guidance.^[6]

Data Currency and System Limitations That Affect GPS-Contingency Planning

If you rely on an onboard navigation database to support route guidance, ensure it is current. When an AIRAC cycle changes during flight, operators should have procedures to validate database accuracy. If an amended chart is published for a procedure, or the procedure’s amendment date is on or after the database’s expiration date, the database must not be used to conduct that operation. Out-of-date data combined with GPS loss compounds navigation risk.^[4]
Systems that qualify as suitable RNAV installations in conventional operations include those using TSO-C129/-C145/-C146 equipment installed per AC 20-138 or AC 20-130A, and systems with DME/DME/IRU inputs compliant with AC 90-100A. These details underscore that reliable RNAV performance depends on both appropriate equipment and current data; if GPS is removed from the mix, capability can change significantly.^[4]
In inertial-only scenarios, navigation accuracy decays over time. For example, when Inertial Navigation Systems/Inertial Reference Units are the only source of long-range navigation, a basic RNP 10 time limit of 6.2 hours between position updates applies unless otherwise approved. This principle illustrates that without periodic position updates (such as GPS), drift grows—so plan to use visual fixes and conservative recovery routes if your sUAS must rely on inertial sensing after GPS loss.^[5]

Practical bottom line: Plan, brief, and train for GPS loss as an emergency under §107.49. Know your airspace and hazards, recognize loss-of-signal indications, be ready to hand-fly the intended flight path using visual fixes, and avoid depending on outdated navigation data or on automation that requires GPS to function as expected.

Test Yourself

UA.V.C.K4

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UA.V.C.K3: Loss of aircraft control link and fly-aways.

UA.V.C.K5: Frequency spectrums and associated limitations.