Can anyone identify this plane?

The submission in question presents a common identification challenge encountered by aviation observers and pilots alike: a large, unidentified aircraft operating at cruise altitude that failed to appear on civilian flight tracking platforms such as FlightRadar24. The observer noted the aircraft was substantially louder than typical widebody commercial traffic at similar altitudes, which narrows the field of candidates considerably and points toward military hardware with older, less efficient high-bypass turbofan or turbofan-era powerplants.

The absence of the aircraft from FlightRadar24 is itself a significant data point. Civilian flight tracking services aggregate ADS-B Out transponder broadcasts, which military aircraft routinely suppress or disable during operational flights. U.S. military transport aircraft — including the Lockheed C-5 Galaxy, Boeing C-17 Globemaster III, and KC-135 Stratotanker — frequently operate without ADS-B position reporting when flying domestic training or logistics sorties, particularly when mission profiles or operational security considerations warrant it. The FAA's LADD (Limiting Aircraft Data Displayed) program also allows certain government and sensitive operators to block position data from public aggregators even when transponders are active.

The C-5 Galaxy remains a plausible candidate given the acoustic profile described. The C-5M Super Galaxy, the current operational variant, is powered by four General Electric CF6-80C2 turbofans — the same engine family found on older 747 and MD-11 variants — and at cruise altitudes produces a distinct, resonant low-frequency noise signature that experienced observers often describe as heavier and more pronounced than modern high-bypass commercial engines. The aircraft's enormous wing area and high gross weight also mean it typically operates at lower cruise altitudes than comparably-sized commercial widebodies, which can amplify perceived noise at ground level.

For professional pilots and operators, the broader takeaway is procedural and situational. Military transport aircraft operating without ADS-B or with suppressed transponder data are a routine presence in domestic and international airspace, and controllers manage their separation through radar surveillance and coordination rather than ADS-B reliance. Flight crews operating under ADS-B In equipped glass panels should understand that traffic advisories generated by TIS-B and FIS-B systems will not reflect non-participating military traffic, reinforcing the continued importance of visual scanning and ATC traffic calls regardless of cockpit traffic display capabilities. This limitation is especially relevant for Part 91 and 135 operators flying in Class A and high-altitude transition airspace where military heavies commonly transit.