What term describes when two hands on an engine/rotor tachometer are superimposed over each other?

What term describes when two hands on an engine/rotor tachometer are superimposed over each other?

• A. Married Needles
• B. Lead and Lag
• C. NAVAID
• D. Mast Bumping

Answer: (A)

When two indicators on a dual-needle tachometer line up exactly, pilots call that condition “married needles.” On rotorcraft, the tachometer often shows two RPM readings—engine RPM and rotor RPM—each with its own needle. If those needles coincide, they visually merge into one, and the term used to describe that overlap is married needles. This is just a descriptive label for the exact alignment of the two readings on the same dial. The other terms don’t describe this visual phenomenon. Lead and lag refer to timing differences in system response, NAVAID is a navigation aid, and mast bumping is a dangerous mechanical condition involving rotor clearance.

When two indicators on a dual-needle tachometer line up exactly, pilots call that condition “married needles.” On rotorcraft, the tachometer often shows two RPM readings—engine RPM and rotor RPM—each with its own needle. If those needles coincide, they visually merge into one, and the term used to describe that overlap is married needles. This is just a descriptive label for the exact alignment of the two readings on the same dial.

The other terms don’t describe this visual phenomenon. Lead and lag refer to timing differences in system response, NAVAID is a navigation aid, and mast bumping is a dangerous mechanical condition involving rotor clearance.