Standard Instrumentation
CFR 91.205 Subpart C delineates the required equipment, instrumentation and certifications for differing flight conditions. The most basic set of flight rules is VFR, or visual flight rules. Although our interest here is IFR, it is important to note that the set of equipment required for IFR flight is in addition to VFR flight requirements. Minimum instrumentation for VFR are an airspeed indicator, and altimeter, a magnetic direction indicator (compass), a fuel gauge for each tank and landing gear position indicator for retractable landing gear. Additionally, there must be a tachometer, pressure and temperature gauge for each engine.
IFR-specific requirements
Flying in bad visibility conditions reduces the effectiveness of VFR and requires more dependence on instrumentation. Additional requirements for IFR flight are two-way radio communication, rate-of-turn indicator, an altimeter-encoder, clock, artificial horizon or attitude indicator, slip/skid indicator and a gyroscopic direction indicator.
Additional Considerations
Additional equipment and instrumentation may be required for aircraft operating at night, at altitudes above 24,000 feet or if operating commercially or under hire.