We continue with Part II of Almon Gray’s comprehensive analysis of Amelia Earhart’s radio communications and lack of same during her final flight. Bill Prymak, Amelia Earhart Society founder and president, has called Gray’s analysis of Earhart’s radio problems during her last flight “one of the finest pieces of work ever presented on this subject.”
“Amelia Didn’t Know Radio,” Part II
by Almon Gray
Precisely what happened next remains unknown, but it appears that Earhart conferred with a local aeronautical communication specialist to get information she could use to base a reply to [Richard] Black. A plan was developed that fulfilled her requirements with a minimum of receiver tuning on her part. The Ontario and the Itasca were to transmit on the same frequency but at different times, and each would transmit a distinctive Morse identification signal. The Ontario’s identifier was “N” and the Itasca’s was “A.”
(These were the characters used to identify the quadrants at the four-course radio ranges, then the principal navigation aid in the United States. Hence, Earhart was familiar with them.)
In 1937 it was still common to describe radio emissions in wavelengths expressed in meters, rather than in frequencies expressed in cycles per second. It seems apparent that the specialist did this during his discussions with Earhart and that he suggested that the ships transmit beacon signals on wavelengths as follows:
– Ontario 750 meters (400 kcs)
– Swan 900 meters (333 kcs)
– Itasca 750 meters (400 kcs)
These were excellent choices. All were allocated internationally for aeronautical radio navigation and were ideal for use with the direction finder in the Earhart plane.
Unfortunately, Earhart did not understand the relationship between wavelength and frequency nor how to convert from one to the other. Consequently, when she replied to Black on 27 June, she confused the figures and unwittingly specified incorrect frequencies for the Swan and the Itasca; she was correct with the Ontario.
In the case of the Swan, she apparently confused the wavelength and frequency figures, and specified that the Swan transmit on 900 kcs (rather than 333 kcs). This was a bad error in that 900 kcs was in the broadcast band and not available for aeronautical use. It also was inferior to the intended frequency of 333 kcs for DF purposes. It was not necessarily devastating, however, and fair bearings probably could have been taken on it with the aircraft DF.
In the Itasca’s case, however, it was to have grave consequences when she again apparently reversed the numbers and told Black to use 7.50 mcs (rather than 400 kcs) on the Itasca. The 7.50 mcs frequency was so high that there was practically no possibility of obtaining usable radio bearings on it with the aircraft DF.
Following is the text of Earhart’s reply to Black, sent the day before she left Bandoeng for Koepang and Darwin:
From: Earhart via RCA Manila & NPM Navy Radio Honolulu
To: Itasca (Black) June 27, 1937 [Java Date; it was 26 June on Howland east of the International Date Line]
SUGGEST ONTARIO STANDBY ON 400 KILOCYCLES TO TRANSMIT LETTER N FIVE MINUTES ON REQUEST WITH STATION CALL REPEATED TWICE END OF EVERY MINUTE STOP SWAN TRANSMIT VOICE NINE MEGACYCLES OR IF I UNABLE RECEIVE READY ON 900 KILOCYCLES STOP ITASCA TRANSMIT LETTER A POSITION OWN CALL LETTERS AS ABOVE ON HALF HOUR 7.5 MEGACYCLES STOP POSITION SHIPS AND OUR LEAVING WILL DETERMINE BROADCASTING SPECIFICALLY STOP IF FREQUENCIES MENTIONED UNSUITABLE NIGHT WORK INFORM ME LAE STOP I WILL GIVE LONG CALL BY VOICE THREE ONE NAUGHT FIVE KCS QUARTER AFTER HOUR POSSIBLY QUARTER TO [signed] EARHART
Had normal air-to-surface communications existed with the Itasca as Earhart approached Howland, the homing problem could almost certainly have been solved quickly. The ship could have told her to home on 500 kcs, the frequency already being transmitted (in addition to 7.50 mcs), and she should have been able to get bearings that would have led her to the ship. Unfortunately, she was unable to hear signals from the Itasca on 3105 kcs, although the ship was hearing her well. It was thus impossible for the Itasca and Earhart to coordinate their actions.
THE AIR-TO-SURFACE COMMUNICATION PROBLEM: A report by Guinea Airways Ltd. shows that Earhart’s radio gear was checked at Lae by one of its wireless operators, H.J. Balfour, and found satisfactory. Good two-way communication was maintained during a 30-minute test hop at Lae, although a roughness in the transmitted voice signal made Earhart difficult to understand. Balfour told her that her speech might be more intelligible if she spoke in a higher pitch while transmitting.
After the flight left Lae for Howland, two-way communication with Lae was maintained until about 0720 2 July Greenwich Mean Time (GMT) [now Universal Coordinated Time], when she shifted to her 3105 kcs night frequency. Several times throughout the night she was heard broadcasting at the prearranged times by stations on Nauru Island and the Itasca, but little of her transmissions were intelligible. Nauru, and later the Itasca, called her numerous nines, but there is no indication that she heard any of the calls. At 1515 GMT, the Itasca picked up Earhart calling to say she would listen on 3105 kcs on the hour and half-hour. At 1744 GMT she asked the Itasca for a bearing, to be taken then and given to her on the hour. She then whistled into the microphone on 3105 kcs to create a signal on which the bearing could be taken. The DF operator on Howland heard this signal but was unable to get a bearing. He remarked that the signal had very little carrier and seemed over-modulated. The plane made no response to numerous calls from the Itasca at this time.
At 1815 GMT Earhart again asked the Itasca for a bearing. She wanted it taken then and reported to her in a half hour (at 1845 GMT), and she whistled into the microphone to provide a signal; she said they were about 100 miles out. Again the Howland DF heard her signal but was unable to get a hearing, and again Earhart made no response to numerous calls from the Itasca. At 1912 GMT, Earhart transmitted the following to the Itasca on voice radio:
WE MUST BE ON YOU NOW BUT CANNOT SEE YOU. RUNNING OUT OF GAS. ONLY ONE HALF HOUR LEFT. BEEN UNABLE TO REACH YOU BY RADIO. WE ARE FLYING AT ONE THOUSAND FEET.
The Itasca was on the correct frequency and putting out strong signals at the time — even San Francisco picked them up. In turn, the aircraft’s signals were very strong when the Itasca picked up her transmission; it was obvious that the aircraft’s fixed antenna and its feeder to the transmitter were still intact. Thus Earhart’s transmission “BEEN UNABLE TO REACH YOU BY RADIO” clearly indicates that her receiving system had failed, probably early in the flight. Beyond that there was no clue as to the nature of the failure — but the clue was not long in coming.
After twice failing to obtain a bearing from the Howland DF on 3105 kcs, Earhart tried to home on the Itasca radio beacon using the aircraft’s direction finder. At 1925 GMT she broadcast to the Itasca:
WE ARE CIRCLING BUT CANNOT HEAR YOU. GO AHEAD ON 7500 NOW OR ON THE SCHEDULE TIME ON HALF HOUR.
By “7500” she was referring to 7500 kcs, the radio beacon frequency she had specified for the Itasca. The ship complied immediately and transmitted the specified beacon signal — Morse “A” on 7500 kcs. The transmitter had no voice capability, so it was impossible to talk to the plane on that frequency. Earhart responded at once on 3105 kcs, saying:
WE RECEIVED YOUR SIGNALS ON SEVENTY FIVE BUT UNABLE TO GET A MINIMUM. PLEASE TAKE BEARINGS ON US AND ANSWER THREE FIVE NAUGHT FIVE (3105 intended) WITH VOICE.
This was followed by a series of long dashes. No bearing was taken and there was no reply to the Itasca’s subsequent transmission.
Earhart obviously picked up the Itasca’s 7500 kcs beacon signals on the aircraft’s loop antenna, because she reported being “Unable to get a minimum,” (the indication of a bearing) and she would not have expected to get a minimum except with a loop antenna. That she heard the signal indicates her receiver was functioning on at least one band. It was uncommon for only a single band to fail; usually, if one failed, they all failed, and so it is quite likely that the receiver was also functioning on the frequency band containing 3105 kcs. Under existing conditions, Earhart should have been able to hear both signals on the loop and on the fixed antenna. She did hear 7500 kcs on the loop, where signals went directly from loop to receiver, but she did not hear 3105 kcs on the fixed antenna, where the incoming signals had to pass through the send-receive relay before reaching the receiver. It is probable, therefore, that the relay had been damaged by lightning or static discharge so that the contacts were not closing properly on the receive side, thus leaving the receiver without an antenna.
No more requests for a bearing were heard. At 2013 G.MT Earhart came up on 3105 kcs, gave a line of position, and said she was shifting to 6210 kcs; that was the last time the Itasca heard signals from the plane.
Had Earhart been more familiar with her radio gear and manipulated the antenna selector switch on the receiver to transmit on the fixed antenna, but receive on the loop, she probably would have established two-way communication with Itasca. She apparently did not attempt it.
End of Part II.
Once again I’m privileged to offer yet another erudite presentation on radio and Amelia Earhart by the late Almon A. Gray, this one titled “Amelia Didn’t Know Radio.” This article initially appeared in the November 1993 edition of U.S. Naval Institute History magazine before Bill Prymak presented it in the December 1993 issue of his Amelia Earhart Society Newsletters.
After graduating from the George Stevens Academy in 1928 and the Massachusetts Radio Telegraph School in 1930, Gray enlisted in the Navy, where he was a radioman and gunner aboard cruiser-based aircraft, and he also learned to fly.
Following his Navy enlistment he joined Pan American Airways, and in 1935 helped build the bases to support the first trans-Pacific air service, and was first officer-in-charge of the PAA radio station on Wake Island. After the San Francisco-Hong Kong air route was opened in late 1935, he was a radio officer in the China Clipper and her sister flying boats. Later he was assistant superintendent of communications for PAA’s Pacific Division. Gray, who flew with Fred Noonan, was a Navy Reserve captain and a major figure in the development of the Marshall Islands landing scenario. He died at 84 on Sept. 26, 1994 at Blue Hill, Maine
This is the first of a three-part presentation. Boldface emphasis mine throughout.
“Amelia Didn’t Know Radio”
by Captain Almon A. Gray, U.S. Naval Reserve (Ret.)
Almost certainly, Amelia Earhart could not get a bearing on the radio beacon on the U.S. Coast Guard Cutter Itasca (WPG-321), lying off the beach at Howland Island, rose the frequency that she had designated –7.50 Mcs* — was so high that her direction finder (DF) was inherently incapable of taking bearings on it.
(* Since 1937 the unit of measurement for radio frequencies has been changed from “cycles” to Hertz (Hz), consequently Megacycles (MCs) and MegaHertz (MHz) will be used interchangeably , as will Kilocycles and Kilohertz (kHz).)
That Earhart and Fred Noonan failed to reach Howland Island on their 1937 around-the-world flight because of radio problems has been studied before — but little has been written about the specifics.
A failure in the plane’s antenna system, which made it impossible to receive signals on the fixed antenna, also was a factor. Had she or Noonan known enough about the system to work around the failure, they could have established voice communications with the Itasca, where someone surely would have suggested they try taking bearings on the vessel’s 500-kilocycle beacon. It could have made all the difference.
BACKGROUND: In early 1937, several weeks before departing Oakland, California, for Honolulu — the first leg of an intended west-about flight around the world — Earhart met at Alameda, California with George Angus, the Superintendent of Communications for the Pacific Division of Pan American Airways (PAA). Angus directed the radio communication and DF [direction finding] networks that supported the PAA clippers on their Pacific crossings, and she was looking for help to augment Noonan’s celestial navigation.
The airline then had specially designed versions of the Adcock radio DF system in service at Alameda, Mokapu Point on Oahu in the Territory of Hawaii, Midway Island, Wake Island, Guam, and Manila in the Philippines. They could take bearings on frequencies much higher than could conventional loop-type direction finders — like Earhart’s — and were effective over much greater distances. These high frequency DFs were the only ones of their type in the United States and its territories. Angus agreed to help and went to work on the details.
This was complicated inasmuch as PAA could receive but not transmit on either of Earhart’s communications frequencies — 3105 or 6210 kHz — and could not transmit voice on any frequency. Earhart and Angus decided that the aircraft would request a bearing by voice on the frequency in use — usually 3105 kHz at night and 6210 kHz during the day — and follow the request with a series of long dashes lasting in the aggregate a couple of minutes.
The PAA DF station would rake a bearing on the transmission and transmit it to the plane on another previously agreed upon PAA frequency, using continuous wave (CW) telegraphy sent at such a slow speed that the individual dots and dashes could be copied on paper and later translated into numbers.
This arrangement was tested on the flight from Oakland to Honolulu; PAA took the bearings on 3105 KHz and transmitted the bearings in Morse code on 2986 KHz. The flight was handled much the same as a routine Clipper flight. Captain Harry Manning, former captain of the SS Roosevelt,the ship that brought her home from Europe after her 1928 trans-Atlantic flight — and a long-time friend, was an experienced radio operator and handled the Electra’s radio and DF gear while regular PAA professional radio operators manned the ground stations. Radio bearings furnished the plane at frequent intervals, first from Alameda and later from Mokapu Point, checked well with the positions Noonan determined by celestial navigation. Nearing Oahu, Manning set up the plane’s DF to home on the 290 kHz marine radio beacon at Makapu Point, near Diamond Head, and Earhart homed in on it to a successful landfall.
While attempting takeoff for Howland-Island from Luke Field, near Honolulu, on March 20, 1937, Earhart ground-looped the Electra, damaging it to the extent that it was shipped back to the Lockheed plant in California for repairs. The radio gear sustained no major damage, but the Western Electric Model 20B radio receiver and its remote-control apparatus were replaced by a Bendix aircraft radio receiver and accessories. The stub mast supporting the V-shaped fixed antenna also was moved a bit forward, and the antenna feed line was rerouted. The late Joseph Gurr, then a moonlighting United Airlines technician, did the work.
THE NEW RECEIVER: The receiver installed at Lockheed was an experimental model incorporating the latest improvements. Only three experimental units were built, although Bendix later marketed an almost identical design as the Type RA-1 Aircraft Radio Receiver.
The experimental model was a continuous turning superheterodyne that covered the spectrum from 150 to 10,000 kcs in five bands. It could receive voice, CW, or modulated CW (MCW) signals and could be controlled remotely from the cockpit. A switch permitted the operator to connect the receiver to either the conventional wire antenna or the loop antenna. When the loop was used, the combination became an effective radio DF system capable of accurate bearings on frequencies between 150 and approximately 1800 kcs. Signals on frequencies higher than 1800 kcs could be heard, but very seldom could accurate bearings be obtained. Earhart was apparently unaware of this. The receiver was powered by a dynamotor operated by storage batteries charged by the main engines.
THE RADIO SYSTEM: When the plane left the Lockheed plant, the radio system consisted of the following elements:
– The experimental Bendix aircraft radio receiver.
– Western Electric Model 13-C 50-watt aircraft transmitter with three crystal-controlled channels: 500, 3105, and 6210 kHz — capable of voice or CW transmissions. It was mounted in the cabin, but there were remote controls in the cockpit.
– A prototype of a Bendix Type MN-20 rotatable shielded loop antenna. It was mounted on the fuselage above the cockpit; the knob that rotated it was on the cockpit overhead between the pilots. It was used primarily for taking radio bearings but was useful as a receiving antenna in static caused by heavy precipitation.
– Fittings at each side of the cockpit for connecting a microphone, headphones, and telegraph key.
– A telegraph key and a jack for connecting headphones at the navigator’s table.
– A 250-foot flexible-wire trailing antenna on an electrically operated, remote-controlled reel at the rear of the plane. The wire exited the lower fuselage through an insulated bushing and had a lead weight, or “fish,” at the end to keep it from whipping when deployed. A variable loading coil used in conjunction with this antenna permitted its use on 500 kHz., and the antenna was long enough to give excellent radiation efficiency on all three transmitting frequencies.
– A fixed, Vee-configured wire antenna with its apex at a stub mast mounted on the top of the fuselage, over the center section of the wing, and its two legs extending back to the two vertical tail fins. The antenna was so short that its radiation efficiency was extremely low; it was adequate for local communications around an airport when it was not feasible to have the trailing antenna deployed, but not for the long-distance communication Earhart required for her transoceanic flight.
Either wire antenna could be selected from the cockpit. The one selected both transmitted and received by means of a send-receive relay that switched the antenna from the receiver to the transmitter when the microphone button was depressed, and switched it back to the receiver when the button was released.
MISTAKES AT MIAMI: After deciding to change her route to east-about, in late May 1937 Earhart flew the plane to Miami, where she had the trailing antenna and associated gear removed completely. John Ray, an Eastern Airlines technician who had his own radio shop as a sideline, did the work. Once again, Amelia obviously did not comprehend the devastating impact this would have on her ability to communicate and to use radio navigation. With only the very short fixed antenna remaining, virtually no energy could be radiated on 500 KHz. This not only foreclosed any possibility of contacting ships and marine shore stations but precluded ships — most important, the Itasca — and marine shore-based DF stations from taking radio bearings on the plane, inasmuch as 500 kHz was the only one of her frequencies that fell within the range of the marine direction finders. Any radio aid in locating Howland Island would have to be in the form of radio bearings taken by the plane on radio signals from the Itasca. Earhart had cut her options severely.
The shortness of the remaining antenna also drastically reduced the power radiated on the two high frequencies. Paul Rafford Jr., a NASA expert in this field involved in forecasting long-range communication requirements to support astronaut recoveries, estimated that the radiated power on 3105 KHz. was about one-half watt. This obviously was a tremendous handicap in the high static level of the tropics.
The fixed antenna also may have been at least partly responsible for the distortion in Earhart’s transmitted signals reported by the operators at Lae, New Guinea, and Howland as affecting the intelligibility of her voice transmissions. A mismatch between the antenna and the final amplifier of a WE-13C transmitter could cause the transmitter to over-modulate and thus introduce distortion.
After a few days in the Pan American Airways shops during which all systems, including the antennas, were tuned and peaked, the plane departed Miami on June 1, 1937 to resume the flight around the world.
Despite these shortcomings, Earhart got as far as the Dutch East Indies without major incident. There, however, because of her unfamiliarity with radio matters, she unwittingly made the mistake that ultimately led to her failure to reach Howland Island.
THE FAULTY PLAN: The legs from New Guinea to Howland Island and from Howland to Hawaii were the most difficult navigational portions of the flight, and three small vessels were stationed along the way to assist. Each planned to use the ship’s transmitter as a radio beacon for Earhart and Noonan to supplement Noonan’s celestial navigation.
– The USS Ontario (AT-13) was on station midway between Lae and Howland.
– The USS Swan (AVP-34) was positioned midway between Howland and Hawaii.
– The USCGC Itasca was at Howland. Her beacon was particularly important; should Noonan’s celestial navigation not put them within visual range of the small, low-lying island, homing in on the Itasca’s signal would be their only chance.
By June 23 these vessels were on or approaching their respective stations but had not been issued their radio beacon frequency or procedures. That day, in a message addressed to Earhart at Darwin or Bandoeng. Richard Black — Earhart’s representative on board the Itasca — advised her of the radio frequencies available on the three ships and asked her to designate the frequency she wished each ship to use when transmitting beacon signals. This message caught up with Earhart at Bandoeng, Java.
(End of Part I.)
The lengthy “The PAA Post-Flight Radio Intercepts” (What they really tell us and what was the U.S. Government trying to cover up?? Why did they want all copies destroyed?” that appeared in the November 1997 issue of Amelia Earhart Society Newsletters is too dense for normal reading and not suitable for this blog.
The important aspects of its bulky contents are covered extensively in the April 30, 2014, “Earhart’s “post-loss” messages: Real or fake?” May 13, 2014, “Experts weigh in on Earhart’s post-loss messages,“ and May 27, 2014, “Amelia Earhart’s alleged “Land in sight” message remains a curiosity, if not a mystery.”
Today we present Bill Prymak’s “Follow-Up on the PAA Post-Flight Radio Intercepts,” which includes his and other researchers’ analyses; it appeared in the March 1998 edition of the Amelia Earhart Society Newsletters. For enhanced realism, I’ve presented this article in its original AES Newsletter format. To read larger version, please left click on the image.
For further discussion, see Amelia Earhart: The Truth at Last, Chapter III, “The Search and the Radio Signals,” pages 40-59.