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MSL (Mean Sea Level)
A measurement of altitude expressed in feet above the average level of the ocean surface. MSL altitude is used for en route navigation, airspace boundaries, and instrument approach procedures. Altimeters display MSL altitude when set to the local altimeter setting.
Related Terms
- Multi-Engine RatingAn add-on rating to a pilot certificate that authorizes the pilot to fly aircraft with more than one engine. Training focuses on engine-out procedures, Vmc demonstrations, asymmetric thrust management, and multi-engine systems.
- NAVAID (Navigational Aid)A ground-based or space-based facility that supports aircraft navigation, such as a VOR, NDB, DME, ILS, or the GPS satellite constellation. NAVAID outages published in NOTAMs can force a route, approach, or training-plan change even when weather looks fine.
- Night CurrencyThe recent flight experience required to carry passengers at night. Under 14 CFR 61.57(b), a pilot needs three takeoffs and three landings to a full stop within the preceding 90 days, accomplished during the period from one hour after sunset to one hour before sunrise.
- Non-Precision ApproachAn instrument approach procedure that provides lateral guidance to the runway but does not include an electronic glideslope for vertical guidance. Examples include localizer-only, VOR, and many RNAV (GPS) LNAV approaches; pilots descend to a minimum descent altitude (MDA) and must see the runway environment to continue.