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Amelia Earhart Search Forum => General discussion => Topic started by: Ric Gillespie on January 08, 2016, 10:42:37 AM
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As part of the research for the new Electra book, Bob Brandenburg and I have been trying to pin down how the radio systems aboard NR16020 evolved over time and exactly what radios were present for the second world flight attempt. It's an important question because Earhart's failure to find Howland was essentially a failure of radio navigation.
In piecing together what happened we've uncovered another mystery and I'm hoping the Forum can help us. Here's a quick overview. (Sorry if this gets a bit down-in-the-weeds but there's no avoiding the technical aspects of the problem.)
In Burbank, on or about March 7, 1937 as NR16020 was being prepared for a planned March 15 departure from Oakland, the Hooven Radio Compass (installed back in October) was removed and replaced with a Bendix loop, loop coupler, and receiver. The loop and loop coupler appear to have been a Navy RDF-1 system and the receiver seems to have been an early version of the RA-1. This new receiver was installed on top of the fuel tanks behind the cockpit bulkhead behind the copilot - the same location where the Hooven receiver had been situated.
One advantage of the new receiver was that it covered 500 kHz, the marine calling and emergency frequency. The Western Electric 20B receiver under the copilots seat did not include that frequency. In February, W.C. Tinus at Bell Labs had convinced Earhart that it would be good if she could communicate with ships on 500 kHz and he had modified her Western Electric 13C transmitter to include a 500 kHz crystal. 500 kHz requires a long antenna and the airplane was equipped with a trailing wire for that purpose. 500 kHz is also a code-only frequency but Earhart had Harry Manning aboard as navigator and radio operator. Manning was adept at Morse code.
With the new receiver Manning would have two-way communication in code with ships at sea.
Helping Earhart with radio matters at this time was United Airlines technician Joe Gurr. Gurr later said that he helped Manning learn how to use the Bendix DF system but had little luck getting Earhart to pay attention long enough to really become familiar with it.
Manning left the team after the accident at Luke Field. Gurr later said that he reinstalled the radios in early May while the plane was in the Lockheed repair shop. Gurr was under the impression that the plane had the same radios aboard for the second world flight attempt as for the first. Based primarily on Gurr, Elgen Long was quite sure there was a Bendix receiver aboard for the second attempt. That does not seem to be the case. In the time between when Gurr reinstalled the radios in early May and when the plane came out of the shop on May 19 the Bendix receiver was apparently removed and the loop and loop coupler were attached to the Western Electric 20B receiver. There are two sources to support this conclusion:
1. A statement made by Chicago Tribune reporter and Earhart friend Carl B. Allen in a manuscript reportedly now in the Smithsonian National Air & Space Museum archives. The following is from East to the Dawn - the Life of Amelia Earhart by Susan Butler (page 387):
"When Allen first arrived in Miami and caught up with Amelia at the airport, one of the first things he did was to go over the equipment list to see if there had been any changes since Oakland. he noted one change that he was;t sure he approved of - the elimination of the marine frequency radio that operated on the 500-kilocycle bandwidth. “Oh,” she said, ‘that was left off when Manning had to drop out of the flight. Both Fred Noonan and I know Morse code but we’re amateurs and probably would never be able to send and receive more than 10 words a minute …The marine frequency radio would have been just that much more dead weight to carry and we decided to leave it in California.”
This is an extremely important quote and I want to check the source myself. I’ve put in a request to NASM to confirm that they have the manuscript and whether it’s at the Udvar-Hazy archives at Dulles or at the NASM Library downtown.
2. In "Last Flight, chapter titled Karachi, Earhart described the "Bendix direction finder" as an instrument on her "dash." She says the Western Electric receiver is under the copilots seat. No mention of a separate Bendix receiver. In fact, nowhere in the 1937 literature (Earhart, Chater, etc.) does anyone say anything about a Bendix receiver.
The mystery is who made the changes in those last days before the plane left the Lockheed shop?
As an aside, there is a rather strange quote via Fred Goerner:
"Lieutenant Commander William Van Dusen, U.S. Naval Reserve (ret.) (who worked with Pan American Airways for many years) has written, "The simple reason ships and shore stations were unable to communicate with the Earhart plane or to transmit bearings, is that the radio transmitter for these marine frequencies was left sitting in the corner of a hangar in Miami when Earhart and Noonan left the U.S. At the last minute she decided to leave it behind because it weighed so much: it meant more work paying out and reeling in an aerial line."
It's not clear where Goerner got this. The Bendix radio was a receiver not a transmitter. This may have been the start of the myth that the trailing wire was removed in Miami. Photos of the plane in Burbank prior to departing for Miami clearly show that the trailing wire was already gone.
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Photos of the plane in Burbank prior to departing for Miami clearly show that the trailing wire was already gone.
It's amazing how much can be discovered after all these years!
Looking forward to the new book. :)
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It is not too much of leap to conclude losing Manning killed Earhart.
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It is not too much of leap to conclude losing Manning killed Earhart.
If we're looking for root causes of the tragedy i think we have to start further back. Manning bailed because he lost faith in Earhart's ability to safely operate the airplane. The Luke Field accident had nothing to do with radios. Perhaps the root cause is the simple fact that Earhart was in over her head, as was her habit throughout her flying career, and this time her incredible run of luck ran out.
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Thank you! That's been my opinion for years now (after reading a lot of the content of your site), but it's not a popular one on many fronts.
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This just in:
"This is on file in the NASM Archives and is known as:
Amelia Earhart Collection [Allen], Acc. XXXX-0520
Dates: 1932-1971
Description: Carl B. Allen learned to fly during World War I. He was active in aviation events and as an aviation writer. Allen was the first airmail passenger to make a continuous flight across the continent in 1927 and he made an air tour of South America in 1933. He won the Sportsman Pilots' cup at the National Air Races in 1930. Allen was the aviation editor of several newspapers, including the New York Herald-Tribune, and he wrote several aviation books, including 'ghosting' Clarence Chamberlin's 'Record Flights.' He was also a flight advisor to Amelia Earhart.
This collection consists of correspondence and writings of Mr. C. B. Allen on the disappearance of Amelia Earhart."
Somehow we missed this source. I'll be making a pilgrimage to Udvar-Hazy Center NASM Archives to review the collection for any new nuggets.
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and archived at NASM
This just in:
"This is on file in the NASM Archives and is known as:
Amelia Earhart Collection [Allen], Acc. XXXX-0520
Dates: 1932-1971
Description: Carl B. Allen learned to fly during World War I. He was active in aviation events and as an aviation writer. Allen was the first airmail passenger to make a continuous flight across the continent in 1927 and he made an air tour of South America in 1933. He won the Sportsman Pilots' cup at the National Air Races in 1930. Allen was the aviation editor of several newspapers, including the New York Herald-Tribune, and he wrote several aviation books, including 'ghosting' Clarence Chamberlin's 'Record Flights.' He was also a flight advisor to Amelia Earhart.
This collection consists of correspondence and writings of Mr. C. B. Allen on the disappearance of Amelia Earhart."
Somehow we missed this source. I'll be making a pilgrimage to Udvar-Hazy Center NASM Archives to review the collection for any new nuggets.
I have copied all the Allen material; however, much of the "good stuff" Allen memorialized and found at the Smithsonian can also be found in: Amelia Earhart: A Biography, by Doris Rich, Smithsonian Institution Press 1989.
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I have copied all the Allen material; however, much of the "good stuff" Allen memorialized and found at the Smithsonian can also be found in: Amelia Earhart: A Biography, by Doris Rich, Smithsonian Institution Press 1989.
Rich's book is poorly footnoted and contains many errors.
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Ric,
Re the current subject; I have come to the conclusion by reading past posts on the subject of radios that AE’s final flight had the Western Electric radio as the transmitter radio – is that correct?
Also, I’ve seen pics of the 10E’s panel that shows radio controls that indicate:
MIC on/off and TRANS on/off
Would the following combinations give the results suggested?
MIC on, TRANS off – for intercom purposes without broadcasting outside the aircraft
MIC on, TRANS on – both intercom on and transmission outside the aircraft
Would these switch combinations take the place of a “push-to-talk” mic configuration we use today i.e. when in the Mic on/Trans on you end up with an open mic with no finger pressing a button necessary?
Ted Campbell
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Re the current subject; I have come to the conclusion by reading past posts on the subject of radios that AE’s final flight had the Western Electric radio as the transmitter radio – is that correct?
That is correct. I don't think anybody disputes that.
Also, I’ve seen pics of the 10E’s panel that shows radio controls that indicate:
MIC on/off and TRANS on/off
Would the following combinations give the results suggested?
MIC on, TRANS off – for intercom purposes without broadcasting outside the aircraft
MIC on, TRANS on – both intercom on and transmission outside the aircraft
Would these switch combinations take the place of a “push-to-talk” mic configuration we use today i.e. when in the Mic on/Trans on you end up with an open mic with no finger pressing a button necessary?
I agree that MIKE (sic)/on, TRANS/on might create an "open mic", but if the plane had intercom capability why did AE and FN communicate by means of written notes?
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Ted Campbell's query about the radio panel got me wondering whether that panel was standard for Model 10s or unique to NR16020. Digging back through the records, I discovered that we have an engineering drawing for that panel (see below) Drawing Number 42690. I got it in 2004 from the guys in the restoration shop at the National Museum of Naval Aviation in Pensacola. At that time they were working on finishing the rebuild of Electra c/n 1130 as a replica of NR16020 but the museum abandoned that project and the rebuild was completed as a sort-of replica of the Electra the Navy had as a VIP transport. (The actual Navy airplane is c/n 1052 at the New England Air Museum which has been rebuilt as as Northwest Airways airliner - go figure.)
Anyway, looking through the lists of Lockheed engineering drawings for the Model 10 - both the NASM microfilm and the Lockheed Maintenance Parts Catalog - there is no Part Number 42690. I have no idea where Pensacola got the drawing they gave me but it is clearly the same control panel shown in photos of the NR16020 cockpit. There is no reference to c/n 1055 on the drawing but the drawing was made on July 15, 1936. That's exactly when c/n 1055 was being completed prior to delivery. This looks very much like something that was done specifically for Earhart at her request.
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[Anyway, looking through the lists of Lockheed engineering drawings for the Model 10 - both the NASM microfilm and the Lockheed Maintenance Parts Catalog - there is no Part Number 42690./quote]
Ric,
In aircraft mfg., is the Lockheed part number always associated with the engineering drawing number ??
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In aircraft mfg., is the Lockheed part number always associated with the engineering drawing number ??
The part number IS the drawing number.
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In support of the "second receiver" theory, the response to C.B. Allen's concerns about marine frequency reception may explain these otherwise anomalous Associated Press reports:
“EARHART IN MIAMI ON TEST FLIGHT: Radio Direction Finder Installed in Plane”. [Dateline 5/23/37 Miami FL] “Pan-American Airways loaned her two technicians to install in her plane a radio direction finder similar to those used in South American and Pacific flights.” Source: 5/24/37 Atlanta Constitution
“A radio direction finder has been installed by Pan American technicians.” Source: 5/30/37 New York Times
“Their own mechanics installed the radio direction finder which they developed for their clipper ships…” Source: 6/1/37 New York Times
The standard receiver used in PAA Clippers was "distinguished by its wide frequency range (250 kc to 25 mc), its light weight (6 pounds) and its simplicity of design...". The Clippers were equipped with crossed-loop DF antennas. Source: "Flying the Pacific by Radio" April, 1936 Electronics, p. 7-10.
The Bendix RA-1B receiver weighed 25 pounds. Source: Instruction Book for Models RA-1B, RA-1I and RA-1J Aircraft Radio Receiving Equipment. Bendix Radio, 1941.
But, GP still referred to the DF as a "Bendix beam-finder" in a late June interview. Source: 6/26/37 Atlanta Constitution (United Press)
FWIW
Dan Brown, #2408
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In support of the "second receiver" theory, the response to C.B. Allen's concerns about marine frequency reception may explain these otherwise anomalous Associated Press reports:
If these are all AP reports they probably come from a single reporter. None of the reports quotes a source such as Earhart or "so-and-so spokesperson for Pan American." I don't know what a crossed-loop DF antenna looks like but the only DF antenna on the airplane when it left Miami was the same Bendix loop that was installed back in march. I have a hard time believing that there was a second DF on the airplane that:
1. Was not externally visible.
2. Was not mentioned by Earhart in the Karachi interview in which she described all the plane's radio equipment and its location.
3. Was not mentioned by Sgt. Rose in Darwin when he fixed the fuse on her direction finder (singular)
4. Was not mentioned in Chater's description of the July 1st test flight in Lae.
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There's also this, a direct attribution from a different reporter:
"Minor Repairs to Amelia's Plane" (Dateline Miami FL 5/24/37) "Her husband, George P. Putnam said workmen will make minor repairs in the plane's radio set and install a radio range finder." Source: 5/24/37 San Mateo Times (United Press)
Based on these reports it sure seems that Pan Am technicians installed some sort of radio "finder" between May 24 and May 30. A Pan Am (PAMSCO) DF receiver might have been connectable to the Bendix loop via the loop coupler as easily as the WE20B receiver was, with no changes externally or in the "dash" necessary. Rose fixed the generator, not the receiver, and neither Rose nor Chater had any reason to expect a particular type of DF receiver was aboard.
I know, "seems" and "might have". FWIW
Dan Brown, #2408
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This is interesting. Let's review the sources in chronological order.
5/23/37
“EARHART IN MIAMI ON TEST FLIGHT: Radio Direction Finder Installed in Plane”. [Dateline 5/23/37 Miami FL] “Pan-American Airways loaned her two technicians to install in her plane a radio direction finder similar to those used in South American and Pacific flights.” Source: 5/24/37 Atlanta Constitution
5/24/37
"Minor Repairs to Amelia's Plane" (Dateline Miami FL 5/24/37) "Her husband, George P. Putnam said workmen will make minor repairs in the plane's radio set and install a radio range finder." Source: 5/24/37 San Mateo Times (United Press)
5/30/37
“A radio direction finder has been installed by Pan American technicians.” Source: 5/30/37 New York Times
6/1/37
“Their own mechanics installed the radio direction finder which they developed for their clipper ships…” Source: 6/1/37 New York Times
6/26/37
GP still referred to the DF as a "Bendix beam-finder" in a late June interview. Source: 6/26/37 Atlanta Constitution (United Press)
On 5/23/37 it's a "radio direction finder similar to those used in South American and Pacific flights.”
On 5/24/37 Putnam calls it "a radio range finder."
On 5/30/37 it's a "radio direction finder."
On 6/1/37 "the radio direction finder which [PanAm] developed for their clipper ships"
On 6/26/37 Putnam calls it a "Bendix beam-finder"
A radio direction finder is not the same thing as a "range finder" or a "beam finder." In 1937, U.S. commercial airliners navigated primarily by means of the "radio range" system. The radio range was an aural system in which the pilot listened for either an "N" or an "A" in code to tell he was to the right or to the left of one of four directional "beams" that would lead him to the station. When he was "on the beam" he heard a steady tone. The range did not require a loop antenna.
A radio direction finder was a visual and aural system that was used to home in on a non-directional beacon. The beacon put out a morse code identifier (for example, SYR for Syracuse). The pilot rotated a loop antenna to get a "minimum" signal and a needle on the instrument panel indicated the relative bearing to the beacon.
None of this makes any sense. It's hard to imagine why any special installation would be required for Earhart to use the radio range and it was a uniquely American system, of no use on a world flight. She already had a radio direction finder. Why would she need another one? I think one of the problem we're dealing with is that neither Putnam nor the newspaper reporters understood the terminology.
"The standard receiver used in PAA Clippers was "distinguished by its wide frequency range (250 kc to 25 mc), its light weight (6 pounds) and its simplicity of design...". The Clippers were equipped with crossed-loop DF antennas. Source: "Flying the Pacific by Radio" April, 1936 Electronics, p. 7-10."
We need to find out what a "crossed-loop DF antenna" system looks like and whether it could be installed inside the airplane.
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We need to find out what a "crossed-loop DF antenna" system looks like and whether it could be installed inside the airplane.
Wikipedia, "Direction Finding": (https://en.wikipedia.org/wiki/Direction_finding) "The crossed-loops DF antenna atop the mast of a tug boat."
(https://upload.wikimedia.org/wikipedia/commons/4/4a/20070917-Piraeus-TB_AgiaVarvara.jpg)
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Assuming you got that by Googling "crossed-loop antenna", that one is not installed inside the boat.
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Assuming you got that by Googling "crossed-loop antenna", that one is not installed inside the boat.
Yes, I got that by Googling "crossed-loop antenna." It seemed to me to be a reasonable search term to use to find out the meaning of the phrase.
I've just inserted the caption for the photo.
I agree that it is not "inside the boat." :)
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Ric, I think you have raised an important question here: "She already had a radio direction finder. Why would she need another one?"
Let me follow up on that one with another:
Given the RDF equipment that we suppose they had on board when they departed Burbank or Oakland, do we have any reason to think that any attempts at RDF, during the flights en route to Miami, would have succeeded?
My present understanding is that successful RDF would have been difficult or impossible, using a manually rotated loop antenna to get a null at frequencies much higher than say 500 kc/kh, using the original Western Electric receiver they were left with after the Bendix receiver was removed.
So let’s suppose, just hypothetically, that they had tried and failed with RDF en route to Miami.
Would not that explain their concern to add RDF equipment from Pan Am, if that were feasible?
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According to Elgen Long (The Mystery Solved, Simon & Schuster, 1999) the two radio technicians sent from Pan Am's radio shop at Dinner Key to work on Earhart's radios were Louis Michelfelder and Robert H. Thibert. Long interviewed Thibert on November 2, 1991. Thibert told Long that on May 29 he checked the direction finder on NR1020 by taking bearings on local broadcast radio station WQAM and found "The direction finder gave good bearings with a definite minimum when the loop was swung to point at the station."
Citing his interview with Thibert, Long goes on at great length about problems the Pan Am radio techs had with Earhart's transmitter and what they did to fix it, but there is no mention a problem with the DF, let alone replacing it with a Pan Am unit.
So whom do we believe? Contemporary press reports or the 54 year-old recollections of the technician who actually did the work? Press reports, as we all know, are often wrong, but so are anecdotal recollections. Just as with the patch that replaced the lavatory window, the one type of evidence we have that we can rely upon is photography and photos of the airplane show no change in the DF antenna.
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"The standard receiver used in PAA Clippers was "distinguished by its wide frequency range (250 kc to 25 mc), its light weight (6 pounds) and its simplicity of design...". The Clippers were equipped with crossed-loop DF antennas. Source: "Flying the Pacific by Radio" April, 1936 Electronics, p. 7-10."
We need to find out what a "crossed-loop DF antenna" system looks like and whether it could be installed inside the airplane.
I have attached a figure from the Aug 1935 issue of Popular Aviation, the radio direction finding antenna pictured here uses a tall exterior mast
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That's not it. I found several photos of various Clippers as early as 1935 with the DF loop antenna enclosed in a football-shaped exterior fairing over the cockpit. Will post next week if current Wx hold over ATL ever clears...
Dan Brown, #2408
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Examples of a football-shaped exterior fairing over the cockpits of Clippers, presumed to enclose a DF loop antenna.
Dan Brown, #2408
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Examples of a football-shaped exterior fairing over the cockpits of Clippers, presumed to enclose a DF loop antenna.
Yep, those are all Boeing 314s, first flight June 7, 1938. The football-shaped fairing over the DF loop seems to have appeared about that time. Idon;t think we'll find a football on any airplane much before then. Clearly, mounted a Df loop inside the airplane was not an option.
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The photo I labeled "1935 Clipper" is alleged by the source (found on Pinterest) to be from a family album documenting their summer vacation in 1935. Looks more like a Sikorsky S-42 than a B-314 to me.
Dan Brown, #2408
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The photo I labeled "1935 Clipper" is alleged by the source (found on Pinterest) to be from a family album documenting their summer vacation in 1935. Looks more like a Sikorsky S-42 than a B-314 to me.
I didn't see that one before. Definitely an S-42.
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I just looked at dozens of photos of S-42s and Martin M-130s in "Pan American's Pacific Pioneers" and found only two photos showing a football-type antenna. Both are S-42s.
The photo of Hong Kong Clipper was taken April 23, 1937 and so would be roughly contemporary with Earhart's time in Miami in May.
The photo of Samoan Clipper was taken December 24, 1937.
Both were survey flights, suggesting that Pan Am only equipped their aircraft with DF loops when they were operating outside their own route system.
In any case, NR16020 obviously never had one of these systems.
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My interest in this stems from, "When Allen first arrived in Miami... one of the first things he did was to go over the equipment list to see if there had been any changes since Oakland. He noted one change that he wasn't sure he approved of - the elimination of the marine frequency radio that operated on the 500-kilocycle bandwidth. “Oh,” she said, ‘that was left off when Manning had to drop out of the flight…The marine frequency radio would have been just that much more dead weight to carry and we decided to leave it in California.”
The WE13C transmitter and WE20B receiver weren't left behind, so what marine frequency radio did Allen and AE refer to? Unless they actually meant the trailing antenna only, the only other radio that operated on 500 kHz possible to leave off was the Bendix DF receiver. Thus the possible motive for a light-weight Pan Am installation in Miami.
Not that it ultimately matters much, just trying to weigh the evidence of those contemporary reports versus the possibility that the Bendix DF loop was ever coupled to the WE20B receiver.
Dan Brown, #2408
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I think it’s safe for us to conclude that the RDF equipment with which AE and FN began the second attempt was not replaced by Pan Am equipment. Such a change would very likely have required a change in the external DF loop antenna, which did not happen, as Ric has shown us in the photos.
Moreover, this conclusion is consistent with the much later recollection of the Pan Am technician that he checked the RDF already in the plane and it was working just fine, providing a clear null in the direction of the local commercial radio station. His report was then that AE did not need a new RDF, because the one she already had was working just fine, thank you. If it ain’t broke, don’t replace it.
Note though that the technician had apparently been asked by someone to check out the RDF. And there are those puzzling news reports, at least one attributed to G. P. Putnam, that a Pan Am RDF was being installed or even had already been installed. My guess is that GP was representing to the press as an accomplished fact, something that upon their arrival in Miami he was expecting to occur, but which in fact did not happen -- the replacement of the existing RDF with a Pan Am device. It did not happen because the Pan Am technician reported that there was no need for such a replacement.
Now that guess leads to the question, why would GP have had any such expectation? My further guess is that they had already experienced difficulties with the RDF during one or more of the legs of the shakedown flight to Miami. Those difficulties would have been serious enough to cause Putnam to be anticipating the need for a replacement of the RDF by Pan Am in Miami.
Dan Brown, this was written before I saw your most recent post. You raise a good question, but I will postpone my attempt to answer it until after Ric has had a chance to respond.
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The WE13C transmitter and WE20B receiver weren't left behind, so what marine frequency radio did Allen and AE refer to?
She was referring to the Bendix RA-1 receiver that was installed with the Bendix RDF loop system just prior to the first world flight attempt in March.
The airplane was delivered in July 1936 with a WE13C transmitter and a WE20B receiver. The transmitter had two crystal-controlled frequencies, 3105 and 6210 kHs – standard frequencies for U.S. aircraft. The receiver could receive on four bands, 200-400 kHz; 550-1500 kHz; 1500-4000 kHz; and 4000-10000 kHz. It could NOT receive on 500 kHz.
When delivered, the aircraft had no homing device.
By September 3, the day before the Bendix Trophy race, arrangements had been made for the installation of “a new radio homing device recently perfected by the Bendix aviation interests.” (Source: Arcadia CA Tribune 9/3/36.) The Hooven/Bendix Radio Compass was installed while the aircraft was at Purdue for the month of October.
While the aircraft was on the east coast in February 1937, W.C. Tinus of Bell Labs convinced Earhart that she needed to be able to communicate with ships at sea via the universal 500 KHz calling frequency. That frequency was code-only but AE had recently brought Harry Manning on board and he was adept with code, so no problem. Tinus added a 500 kHz crystal to the WE13C transmitter.
At the same time, Earhart agreed to let Bendix replace the Radio Compass with a Navy RDF loop antenna system that Bendix wanted to introduce for commercial use. It was more complicated to use than the Radio Compass but DF would be Manning's responsibility so, again, no problem. To give the aircraft the capability to receive on 500 kHz, Bendix would install an RA-1 receiver with the new loop system after the aircraft returned to Burbank. The Radio Compass was removed and the RDF and RA-1 were installed in early March.
When Manning bailed after the wreck in Hawaii, communication on code-only 500 kHz was no longer an option so, to save weight, the RA-1 "marine frequency" receiver was removed and the Bendix RDF system was connected to the WE20B.
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...the RA-1 "marine frequency" receiver was removed and the Bendix RDF system was connected to the WE20B.
Agreed that the RA-1 receiver must have been left in Oakland along with the trailing antenna, but how is it known that the Bendix loop and coupler were then connected to the WE20B, rather than to a Pan Am DF receiver installed at the last moment in Miami? There's no dispute that Thibert checked some DF on May 29th but it seems possible it was the just-installed Pan Am one.
I have a hard time getting past that big headline, "Radio Direction Finder Installed in Plane", but I'll let it lay from here forward.
Dan Brown, #2408
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how is it known that the Bendix loop and coupler were then connected to the WE20B, rather than to a Pan Am DF receiver installed at the last moment in Miami?
Good point. It is not known. It's an assumption. This is a real puzzler. If the Bendix loop and coupler were not connected to the WE20B when the RA-1 receiver was removed, then the airplane left California without an operating DF. Why would they do that? Were they counting on getting one from Pan American? Why not use the WE20B?
What if they did connect it to the WE20B but on the trip to Miami they discovered it wouldn't work? Upon arrival in Miami they complain and Pan Am says, "We'll loan you you one of ours."
There's no dispute that Thibert checked some DF on May 29th but it seems possible it was the just-installed Pan Am one.
When C.B Allen arrived in Miami he went over the list of equipment he had made in Oakland before the first attempt. He asked AE to "give me a fill-in on new equipment, if any, that had been added." That's when he noticed that the "marine frequency radio" was missing. No mention of adding a new DF receiver. So the question is, when did Allen interview Amelia? He doesn't mention the date but he says, "The Herald Tribune was informed of Amelia's changed plans and I was dispatched to Miami..." Earhart didn't announce the second attempt until May 29, so that would seem to be the earliest date she could have spoken with Allen.
I have a hard time getting past that big headline, "Radio Direction Finder Installed in Plane", but I'll let it lay from here forward.
I think one of the problems is terminology. The "radio direction finder" is the device that finds direction. It has to be connected to a radio receiver but a receiver is not a direction finder. The Hooven/Bendix Radio Compass incorporated its own receiver. The Bendix RDF loop and coupler did not. As far as we know, the Bendix loop and coupler would work with any standard aircraft receiver. The headline says "Radio Direction Finder Installed in Plane," not "Radio Direction Finder Installed on Plane." The external structure did not change so the headline must be referring to the receiver.