Originally Posted by
boeing_eng
From photographic evidence, the only 707/720s that lacked the HF probe were US domestic aircraft, specifically, American's 720s (but not their 707-120s), United's 720s and TWA's 707-120s. As far as I'm aware all other 707/720s had the probe.
TWA retrofitted a couple of early 707's with tail HF Antennas for transatlantic ops. They were removed when the a/c returned to domestic duties
Some 707's had a second HF Antenna (not probe) on the R/H wing to allow a dual HF set-up
Yes, apologies it's correctly the HF antenna. However, all Monarch's 720Bs had them - the ex Northwest 051Bs and the two ex American 023Bs - so perhaps it was a retrofit in the case of these two?