exitrowaisle
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HF Antenna On 707-100s

Wed Jul 02, 2008 1:37 am

I've seen this topic discussed but not sure if it was answered: both American Airlines and TWA had some 707s with the HF mast antenna on the tail, and some that didn't. I read in another post that all the 707-123s (AA) had the antenna originally, even though the domestic planes didn't need HF. My question is, why did AA and TWA have both types of tail on their domestic 707-100s? Did they all start out with tail antennas, with some removed later? If so, why, and why not all? Thanks!
 
Viscount724
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RE: HF Antenna On 707-100s

Wed Jul 02, 2008 3:28 am

Related question. Some 707s, as far as I can tell only the R-R Conway-powered -420 series, also had a probe antenna on the right wingtip in addition to the one on the tail. All sources I can find refer to the wingtip antenna as an HF antenna. If that's the case, why two HF antennas, assuming the one on the tail was also HF? Both antennas are visible in the following photos of BOAC, Lufthansa and El Al 707-420s, but it's also on -420s of the other original customers for that model (Air India and Varig). I can't find it on photos of any other 707 models.


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411A
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RE: HF Antenna On 707-100s

Thu Jul 03, 2008 1:49 am

Two HF antennas were installed on some B707's for redundancy, as many air routes at the time absolutely required dual HF installations...IE: two HF radios, dual antenna couplers, dual antennas (the latter was a customer option).
IF you have only one HF antenna, and it becomes inop for whatever reason, HF transmissions would therefore not be possible.
 
ImperialEagle
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RE: HF Antenna On 707-100s

Fri Jul 04, 2008 12:26 am



Quoting 411A (Reply 2):
Two HF antennas were installed on some B707's for redundancy

Correct.

I agree----I think all the -420's had them, however there were some (pure-jet) 320's with them too (AF and SN), and some specialized -137's had them-----some of them with one on each trailing wingtip rather than protruding forward.
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jetjack74
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RE: HF Antenna On 707-100s

Fri Jul 11, 2008 3:52 pm

Qantas 707-138/B aircraft also had the fwd stbd wingtip antenne.

Quoting Exitrowaisle (Thread starter):
My question is, why did AA and TWA have both types of tail on their domestic 707-100s? Did they all start out with tail antennas, with some removed later? If so, why, and why not all? Thanks!

Some of the AA 707-123's had them, some didn't. The -123's that did have them were the first models ordered which all had the short fin. In 1960, the shortfin -123s with the HF antennes were given tail fin mods to improve handling on flights and kept the HF antennas, they were also re-engined with JT3D's. The -123s w/o the HF antennas were new-build 123B's ordered without the HF ant becuase they were specified as domestic 707's, therefore no need for HF radios. However, AA seem to remove them and re-install them throughout the use of some individual aircraft The 323B/C aircraft handled the long hauls

At TWA, the -131's w/o the antennas were the -131B's, and like the AA -123B's new-builds, were kept that way while with TWA and were confined to non-overwater flights. Few of them found work with other domestic carriers and were modified. The only 131's that had the HF ariel were the turbojet powered ones (unlike AA, TWA never re-engined those). They had them because, like Pan Am, they originally operated them on transoceanic flights to Europe and Asia when they first came out. When the B's came out, the 100B's were kept state-side along with the early 131's, while the -300, again, like AA's took on the long haul routes

[Edited 2008-07-11 08:56:39]
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Viscount724
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RE: HF Antenna On 707-100s

Fri Jul 11, 2008 6:20 pm



Quoting Jetjack74 (Reply 4):
The -123s w/o the HF antennas were new-build 123B's ordered without the HF ant becuase they were specified as domestic 707's, therefore no need for HF radios. However, AA seem to remove them and re-install them throughout the use of some individual aircraft The 323B/C aircraft handled the long hauls

What AA long hauls are you referring to? When AA took delivery of their -323B/Cs they had no routes outside continental North America. Following is their system route map as of October 1968.
http://www.airchive.com/Timetables%2...merican%20Compressed/AAmap6810.jpg

They did use the -323B/Cs for their brief (1970-75) service to the South Pacific but when they originally ordered the -323s they wouldn't have even known about those routes. AA's -323B/Cs were also unusual (like their -123/-123Bs) in only having 2 turbocompressors. It was my understanding this was because of AA's lack of overwater longhaul routes, since they would generally be within a fairly short diversion distance from an alternate airport in the event of pressurization problems.
 
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jetjack74
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RE: HF Antenna On 707-100s

Fri Jul 11, 2008 9:46 pm

In the 1970's, AA did contract charters and ad-hoc freighter service for the DoD to Europe, Asia and Latin America. The also did charters for public and private companies. I believe AA flew between the mainland to HNL as well in the mid 70's.

Quoting Viscount724 (Reply 5):
AA's -323B/Cs were also unusual (like their -123/-123Bs) in only having 2 turbocompressors. It was my understanding this was because of AA's lack of overwater longhaul routes, since they would generally be within a fairly short diversion distance from an alternate airport in the event of pressurization problems.

A few Pan Am 321C's had this as well, as this example of a former PA 707 shows.

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Anyway, I was told that the #4 turbocompressor on the 707 could be isolated and shut off, so the aircraft could run with 1 or 2 of them to save fuel consumption. So AA went ahead an ordered it without the 3rd one. But it wasn't a requirement to have the a # 4 compressor, it was optional. AA flew dozens of overwater routes with the 707-300B/C over course of their operation.
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Viscount724
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RE: HF Antenna On 707-100s

Fri Jul 11, 2008 11:21 pm



Quoting Jetjack74 (Reply 6):
Quoting Viscount724 (Reply 5):
AA's -323B/Cs were also unusual (like their -123/-123Bs) in only having 2 turbocompressors. It was my understanding this was because of AA's lack of overwater longhaul routes, since they would generally be within a fairly short diversion distance from an alternate airport in the event of pressurization problems.

A few Pan Am 321C's had this as well, as this example of a former PA 707 shows.

Thanks for that information. It looks like a dozen or so Pan Am 321Cs used strictly as freighters (no windows) lacked the 3rd turbocompressor. Those that were convertible and mostly used in passenger service appear to have the 3rd turbocompressor. One photo of each model below, showing the missing turbocompressor on the freighter (first photo).


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