FAA Instrument Flight Instructor (FII)Instrument RegulationsHard
An aircraft's ADF is inoperative, but the published nonprecision approach requires ADF to identify a step-down fix. The aircraft is equipped with an IFR-approved GPS with a current database. According to the AIM, may the pilot use GPS in lieu of the inoperative ADF for this fix?
- AOnly if a second pilot verifies the fix visually using pilotage
- BYes, an IFR-approved GPS may be used to substitute for ADF when flying the procedure
- CNo, GPS may never substitute for ADF under any circumstances
- DOnly if the approach is flown during daylight VFR conditions
Show answer & explanationAnswer & explanation
Correct answer: B. Yes, an IFR-approved GPS may be used to substitute for ADF when flying the procedure
The AIM and associated guidance (e.g., AC 90-108) permit an IFR-approved GPS with appropriate database currency to be used as a substitute for ADF and DME, and in some cases VOR, when flying procedures that would otherwise require those NAVAIDs, provided the aircraft is equipped and approved accordingly. This allows continued use of the procedure despite the ADF malfunction.
Why the other options are wrong
- A. Visual pilotage verification is not the sanctioned substitution method.
- C. GPS substitution is specifically authorized under current AIM/AC guidance.
- D. The substitution is not limited to daylight VFR conditions.
GPS Substitution for ADF/DME
An IFR-approved GPS with a current database may be used in lieu of ADF or DME (and in some cases VOR) for identifying fixes on published procedures, per AIM and AC 90-108 guidance.
- Applies to ADF and DME substitution primarily
- Requires IFR-approved GPS with current database
- Also covered under RNAV substitution rules (AC 90-108)
- Does not require VFR conditions or visual verification
Memory trick: 'GPS steps in when ADF steps out' — modern nav covers old gaps.