Which flight instruments are essential for IFR flying?

For instrument flight rules (IFR) operations, certain flight instruments are critical for ensuring safe navigation and control of the aircraft under instrument conditions. The correct answer identifies a set of instruments that play essential roles in maintaining altitude, attitude, speed, and vertical performance.

The altimeter is vital for reading altitude based on atmospheric pressure, which is crucial for maintaining safe vertical separation from terrain and other aircraft. The artificial horizon (or attitude indicator) provides a visual representation of the aircraft's orientation relative to the horizon, allowing pilots to maintain level flight or execute turns without relying on visual reference outside the cockpit. The airspeed indicator is essential for understanding the aircraft's speed relative to the surrounding air, which is important for performance calculations and aircraft control. The vertical speed indicator shows whether the aircraft is climbing or descending and at what rate, providing critical information for altitude management.

This combination of instruments ensures that pilots can safely conduct flight operations strictly by reference to instruments, which is the fundamental requirement of IFR flying. Moreover, the heading indicator helps maintain course direction but is not explicitly included in the correct answer choice.

The other options suggest combinations of instruments that either include non-essential items for IFR operations or omit key instruments required for safe and effective instrument flight. Thus, the selection