N2

N2 (plural N2s)

1. (aviation) The rotational speed of the high-pressure spool of a two-spool gas turbine engine or the intermediate-pressure spool of a three-spool gas turbine engine, expressed as a percentage of a certain reference rotational speed.
   • 1971 February 3, National Transportation Safety Board, “Analysis and Conclusions”, in Aircraft Incident Report: American Airlines, Inc., Boeing 747-121, N743PA, San Francisco, California, September 18, 1970‎, archived from the original on 5 July 2022, page 12:

     The inputs into the computerized JT9D condition monitoring program for this engine from September 10 through 16 likewise reflected adverse changes in trends of vital operating parameters which were indicative of the possibility of a serious engine malfunction. These data points showed a progressive increase of EGT and fuel flow while N2 showed a progressive decrease over the same period of time.

   • 2007 January 9, National Transportation Safety Board, “1.16.3 Engine Tests”, in Aircraft Accident Report: Crash of Pinnacle Airlines Flight 3701, Bombardier CL-600-2B19, N8396A, Jefferson City, Missouri, October 14, 2004‎, archived from the original on 5 July 2022, page 27:

     A test to evaluate the slight increases (25 to 30 pounds per square inch gauge [psig]) in core-driven hydraulic pump pressure indications showed that hydraulic pump pressure would begin to indicate on the FDR with about 35 rpm of core rotation. Another test showed that N2 signals would begin to indicate on the FDR and in the cockpit with about 70 rpm of core rotation.

2. Alternative form of N₂

• N1
• N3