Amelia Earheart Part II

 

Radio equipment

In preparation for the trip to Howland Island, the U.S. Coast Guard had sent the cutter USCGC Itasca (1929) to the island. The cutter offered many services such as ferrying news reporters to the island, but it also had communication and navigation functions. The plan was the cutter could: communicate with Earhart's aircraft via radio; transmit a radio homing signal to make it easy to find Howland Island without precise celestial navigation; do radio direction finding if Earhart used her 500 kHz transmitter; use an experimental high-frequency direction finder for Earhart's voice transmissions; and use her boilers to "make smoke" (create a dark column of smoke that can be seen over the horizon). All of the navigation methods would fail to guide Earhart to Howland Island.

The Electra had radio equipment for both communication and navigation, but details about that equipment are not clear. The Electra failed to establish two-way radio communications with USCGC Itasca (1929) and failed to radio-locate Itasca. Many explanations have been proposed for those failures.

The plane had a modified Western Electric model 13C transmitter. The 50-watt transmitter was crystal controlled and capable of transmitting on 500 kHz, 3105 kHz, and 6210 kHz. Crystal control means that the transmitter cannot be tuned to other frequencies; the plane could transmit only on those three frequencies. The transmitter had been modified at the factory to provide the 500 kHz capability.

The plane had a modified Western Electric model 20B receiver. Ordinarily, the receiver covered four frequency bands: 188–420 kHz, 550–1500 kHz, 1500–4000 kHz, and 4000–10000 kHz. The receiver was modified to lower the frequencies in the second band to 485–1200 kHz. That modification allowed the reception of 500 kHz signals; such signals were used for marine distress calls and radio navigation. The model 20B receiver has two antenna inputs: a low-frequency antenna input and a high-frequency antenna input. The receiver's band selector also selects which antenna input is used; the first two bands use the low-frequency antenna, and the last two bands select the high-frequency antenna.

It is unknown whether the model 20B receiver had a beat frequency oscillator that would enable the detection of continuous wave transmissions such as Morse code and radio-location beacons. Neither Earhart nor Noonan were capable of using Morse code. They relied on voice communications. Manning, who was on the first world flight attempt but not the second, was skilled at Morse and had acquired an FCC aircraft radiotelegraph license for 15 words per minute in March 1937, just prior to the start of the first flight.

A separate automatic radio direction finder receiver, a prototype Hooven Radio Compass,[156] had been installed in the plane in October 1936, but that receiver was removed before the flight to save weight. The Hooven Radio Compass was replaced with a Bendix coupling unit that allowed a conventional loop antenna to be attached to an existing receiver (i.e., the Western Electric 20B). The loop antenna is visible above the cockpit on Earhart's plane.

Alternatively, the loop antenna may have been connected to a Bendix RA-1 auxiliary receiver with direction finding capability up to 1500 kHz. It is not clear that such a receiver was installed, and if it were, it may have been removed before the flight. Elgen and Marie Long describe Joe Gurr training Earhart to use a Bendix receiver and other equipment to tune radio station KFI on 640 kHz and determine its direction.

Whichever receiver was used, there are pictures of Earhart's radio direction finder loop antenna and its 5-band Bendix coupling unit. The details of the loop and its coupler are not clear. Elgen and Marie Long claim that the coupling unit adapted a standard RDF-1-B loop to the RA-1 receiver, and that the system was limited to frequencies below 1430 kHz. During the first world flight attempt's leg from Honolulu to Howland (when Manning was a navigator), Itasca was supposed to transmit a CW homing beacon at either 375 kHz or 500 kHz. At least twice during the world flight, Earhart failed to determine radio bearings at 7500 kHz. If the RDF equipment was not suitable for that frequency, then attempting such a fix would be operator error and fruitless. However, the earlier 7-band Navy RDF-1-A covered 500 kHz–8000 kHz. The later 3-band DU-1 covered 200 kHz–1600 kHz. It is not clear where the RDF-1-B or Earhart's coupler performance sits between those two units. In addition, the RDF-1-A and DU-1 coupler designs have other differences. The intention is to have the ordinary receive antenna connected to the coupler's antenna input; from there, it is passed on to the receiver. In the RDF-1-A design, the coupler must be powered on for that design function to work. In the later DU-1 design, the coupler need not be powered.

There were problems with the RDF equipment during the world flight. During the transatlantic leg of the flight (Brazil to Africa), the RDF equipment did not work. The radio direction finding station at Darwin expected to be in contact with Earhart when she arrived there, but Earhart stated that the RDF was not functioning; the problem was a blown fuse. During a test flight at Lae, Earhart could hear radio signals, but she failed to obtain an RDF bearing. While apparently near Howland Island, Earhart reported receiving a 7500 kHz signal from Itasca, but she was unable to obtain an RDF bearing.

The antennas and their connections on the Electra are not certain. A dorsal Vee antenna was added by Bell Telephone Laboratories. There had been a trailing wire antenna for 500 kHz, but the Luke Field accident collapsed both landing gear and wiped off the ventral antennas. After the accident, the trailing wire antenna was removed, the dorsal antenna was modified, and a ventral antenna was installed. It is not certain, but it is likely that the dorsal antenna was only connected to the transmitter (i.e., no "break in" relay), and the ventral antenna was only connected to the receiver. Once the second world flight started, problems with radio reception were noticed while flying across the US; Pan Am technicians may have modified the ventral antenna while the plane was in Miami. At Lae, problems with transmission quality on 6210 kHz were noticed. Once the flight took off from Lae, Lae did not receive radio messages on 6210 kHz (Earhart's daytime frequency) until four hours later (at 2:18 pm); Lae's last reception was at 5:18 pm and was a strong signal; Lae received nothing after that; presumably the plane switched to 3105 kHz (Earhart's nighttime frequency). Itasca heard Earhart on 3105 kHz, but did not hear her on 6210 kHz. TIGHAR postulates that the ventral receiving antenna was scraped off while the Electra taxied to the runway at Lae; consequently, the Electra lost its ability to receive HF transmissions.

Nearing Howland Island

The USCGC Itasca was on station at Howland. Its task was to communicate with Earhart's Electra and guide them to the island once they arrived in the vicinity. Noonan and Earhart expected to do voice communications on 3105 kHz during the night and 6210 kHz during the day.

Through a series of misunderstandings or errors (the details of which are still controversial), the final approach to Howland Island using radio navigation was not successful. Fred Noonan had earlier written about problems affecting the accuracy of radio direction finding in navigation. Another cited cause of possible confusion was that the Itasca and Earhart planned their communication schedule using time systems set a half-hour apart, with Earhart using Greenwich Civil Time (GCT) and the Itasca under a Naval time zone designation system.

The Electra expected Itasca to transmit signals that the Electra could use as an RDF beacon to find the Itasca. In theory, the plane could listen for the signal while rotating its loop antenna. A sharp minimum indicates the direction of the RDF beacon. The Electra's RDF equipment had failed due to a blown fuse during an earlier leg flying to Darwin; the fuse was replaced. Near Howland, Earhart could hear the transmission from Itasca on 7500 kHz, but she was unable to determine a minimum, so she could not determine a direction to Itasca. Earhart was also unable to determine a minimum during an RDF test at Lae. One likely theory is that Earhart's RDF equipment did not work at 7500 kHz; most RDF equipment at the time was not designed to work above 2000 kHz. When operated above their design frequency, loop antennas lose their directionality.

Itasca had its own RDF equipment, but that equipment did not work above 550 kHz, so Itasca could not determine the direction to the Electra's HF transmissions at 3105 and 6210 kHz. The Electra had been equipped to transmit a 500 kHz signal that Itasca could use for radio direction finding, but some of that equipment had been removed. The equipment originally used a long trailing wire antenna. While the plane was in flight, the wire antenna would be paid out at the tail; efficient transmissions at 500 kHz needed a long antenna. The antenna was bulky and heavy, so the trailing wire antenna was removed to save weight. If nothing else had been done, the plane would have been unable to transmit an RDF signal that Itasca could use. Such a modification was made, but without voice communication from Itasca to the plane, the ship could not tell the plane to use its 500 kHz signal. Even if Itasca could get a bearing to the plane, the Itasca could not tell the plane that bearing, so the plane could not head to the ship.

Some sources have noted Earhart's apparent lack of understanding of her direction-finding system, which had been fitted to the aircraft just prior to the flight. The system was equipped with a new receiver from Bendix that operated on five wavelength "bands", marked 1 to 5. The loop antenna was equipped with a tuneable loading coil that changed the effective length of the antenna to allow it to work efficiently at different wavelengths. The tuner on the antenna was also marked with five settings, 1 to 5, but, critically, these were not the same frequency bands as the corresponding bands on the radio. The two were close enough for settings 1, 2 and 3, but the higher frequency settings, 4 and 5, were entirely different. The upper bands (4 and 5) could not be used for direction finding. Earhart's only training on the system was a brief introduction by Joe Gurr at the Lockheed factory, and the topic had not come up. A card displaying the band settings of the antenna was mounted so it was not visible. Gurr explained that higher frequency bands would offer better accuracy and longer range.

Motion picture evidence from Lae suggests that an antenna mounted underneath the fuselage may have been torn off from the fuel-heavy Electra during taxi or takeoff from Lae's turf runway, though no antenna was reported found at Lae.

Radio signals

During Earhart and Noonan's approach to Howland Island, the Itasca received strong and clear voice transmissions from Earhart identifying as KHAQQ, but she apparently was unable to hear voice transmissions from the ship. Signals from the ship would also be used for direction finding, implying that the aircraft's direction finder was also not functional.

The first calls, routine reports stating the weather as cloudy and overcast, were received at 2:45 and just before 5 am on July 2. These calls were broken up by static, but at this point the aircraft would still be a long distance from Howland.

At 6:14 am another call was received stating the aircraft was within 200 miles (320 km), and requested that the ship use its direction finder to provide a bearing for the aircraft. Earhart began whistling into the microphone to provide a continual signal for them to home in on. It was at this point that the radio operators on the Itasca realized that their RDF system could not tune in the aircraft's 3105 kHz frequency; radioman Leo Bellarts later commented that he "was sitting there sweating blood because I couldn't do a darn thing about it." A similar call asking for a bearing was received at 6:45 am, when Earhart estimated they were 100 miles (160 km) out.

An Itasca radio log (position 1) at 7:30–7:40 am states:

EARHART ON NW SEZ RUNNING OUT OF GAS ONLY 1/2 HOUR LEFT CANT HR US AT ALL / WE HR HER AND ARE SENDING ON 3105 ES 500 SAME TIME CONSTANTLY

Another Itasca radio log (position 2) at 7:42 am states:

KHAQQ [Earhart's plane] CLNG ITASCA WE MUST BE ON YOU BUT CANNOT SEE U BUT GAS IS RUNNING LOW BEEN UNABLE TO REACH YOU BY RADIO WE ARE FLYING AT A 1000 FEET

Earhart's 7:58 am transmission said she could not hear the Itasca and asked them to send voice signals so she could try to take a radio bearing. This transmission was reported by the Itasca as the loudest possible signal, indicating Earhart and Noonan were in the immediate area. They could not send voice at the frequency she asked for, so Morse code signals were sent instead. Earhart acknowledged receiving these but said she was unable to determine their direction.

In her last known transmission at 8:43 am Earhart broadcast "We are on the line 157 337. We will repeat this message. We will repeat this on 6210 kilocycles. Wait." However, a few moments later she was back on the same frequency (3105 kHz) with a transmission that was logged as "questionable": "We are running on line north and south." Earhart's transmissions seemed to indicate she and Noonan believed they had reached Howland's charted position, which was incorrect by about five nautical miles (10 km). The Itasca used her oil-fired boilers to generate smoke for a period of time, but the fliers apparently did not see it. The many scattered clouds in the area around Howland Island have also been cited as a problem: their dark shadows on the ocean surface may have been almost indistinguishable from the island's subdued and very flat profile.

Whether any post-loss radio signals were received from Earhart and Noonan remains unclear. If transmissions were received from the Electra, most if not all were weak and hopelessly garbled. Earhart's voice transmissions to Howland were on 3105 kHz, a frequency restricted in the United States by the FCC to aviation use. This frequency was thought to be not fit for broadcasts over great distances. When Earhart was at cruising altitude and midway between Lae and Howland (over 1,000 miles (1,600 km) from each) neither station heard her scheduled transmission at 0815 GCT. Moreover, the 50-watt transmitter used by Earhart was attached to a less-than-optimum-length V-type antenna.

The last voice transmission received on Howland Island from Earhart indicated she and Noonan were flying along a line of position (running N–S on 157–337 degrees) which Noonan would have calculated and drawn on a chart as passing through Howland. After all contact was lost with Howland Island, attempts were made to reach the flyers with both voice and Morse code transmissions. Operators across the Pacific and the United States may have heard signals from the downed Electra but these were unintelligible or weak.

Some of these reports of transmissions were later determined to be hoaxes but others were deemed authentic. Bearings taken by Pan American Airways stations suggested signals originating from several locations, including Gardner Island (Nikumaroro), 360 miles (580 km) to the SSE. It was noted at the time that if these signals were from Earhart and Noonan, they must have been on land with the aircraft since water would have otherwise shorted out the Electra's electrical system. Sporadic signals were reported for four or five days after the disappearance but none yielded any understandable information. The captain of USS Colorado later said: "There was no doubt many stations were calling the Earhart plane on the plane's frequency, some by voice and others by signals. All of these added to the confusion and doubtfulness of the authenticity of the reports."

Contemporaneous search efforts

Beginning approximately one hour after Earhart's last recorded message, the USCGC Itasca undertook an ultimately unsuccessful search north and west of Howland Island based on initial assumptions about transmissions from the aircraft. The United States Navy (USN) soon joined the search and over a period of about three days sent available resources to the search area in the vicinity of Howland Island. The initial search by the Itasca involved running up the 157/337 line of position to the NNW from Howland Island. The Itasca then searched the area to the immediate NE of the island, corresponding to the area, yet wider than the area searched to the NW. Based on bearings of several supposed Earhart radio transmissions, some of the search efforts were directed to a specific position on a line of 281 degrees (approximately northwest) from Howland Island without evidence of the flyers. Four days after Earhart's last verified radio transmission, on July 6, 1937, the captain of the battleship Colorado received orders from the Commandant, Fourteenth Naval District to take over all naval and coast guard units to coordinate search efforts.

Later search efforts were directed to the Phoenix Islands south of Howland Island. A week after the disappearance, naval aircraft from the Colorado flew over several islands in the group including Gardner Island (now called Nikumaroro), which had been uninhabited for over 40 years. The subsequent report on Gardner read: "Here signs of recent habitation were clearly visible but repeated circling and zooming failed to elicit any answering wave from possible inhabitants and it was finally taken for granted that none were there... At the western end of the island a tramp steamer (of about 4000 tons)... lay high and almost dry head onto the coral beach with her back broken in two places. The lagoon at Gardner looked sufficiently deep and certainly large enough so that a seaplane or even an airboat could have landed or taken-off in any direction with little if any difficulty. Given a chance, it is believed that Miss Earhart could have landed her aircraft in this lagoon and swum or waded ashore." They also found that Gardner's shape and size as recorded on charts were wholly inaccurate. Other Navy search efforts were again directed north, west and southwest of Howland Island, based on a possibility the Electra had ditched in the ocean, was afloat, or that the aviators were in an emergency raft.

The official search efforts lasted until July 19, 1937. At $4 million, the air and sea search by the Navy and Coast Guard was the most costly and intensive in U.S. history up to that time, but search and rescue techniques during the era were rudimentary and some of the search was based on erroneous assumptions and flawed information. Official reporting of the search effort was influenced by individuals wary about how their roles in looking for an American hero might be reported by the press. Despite an unprecedented search by the United States Navy and Coast Guard, no physical evidence of Earhart, Noonan or the Electra 10E was found. The aircraft carrier USS Lexington, the battleship USS Colorado, the Itasca, the Japanese oceanographic survey vessel Koshu, and the Japanese seaplane tender Kamoi searched for six–seven days each, covering 150,000 square miles (390,000 km2).

Immediately after the end of the official search, Putnam financed a private search by local authorities of nearby Pacific islands and waters, concentrating on the Gilberts. In late July 1937, Putnam chartered two small boats, and, while he remained in the United States, directed a search of the Phoenix Islands, Christmas (Kiritimati) Island, Fanning (Tabuaeran) Island, the Gilbert Islands, and the Marshall Islands, but no trace of the Electra or its occupants was found.

Back in the United States, Putnam acted to become the trustee of Earhart's estate so that he could pay for the searches and related bills. In probate court in Los Angeles, Putnam requested to have the "declared death in absentia" seven-year waiting period waived so that he could manage Earhart's finances. As a result, Earhart was declared legally dead on January 5, 1939.

Speculation on disappearance

There has been considerable speculation on what happened to Earhart and Noonan. Most historians hold to the simple "crash and sink" theory, but a number of other possibilities have been proposed, including several conspiracy theories.

Some have suggested that Earhart and Noonan survived and landed elsewhere, but were either never found or killed, making en-route locations like Tarawa unlikely. Proposals have included the uninhabited Gardner Island, 400 mi (640 km) from the vicinity of Howland, the Japanese-controlled Marshall Islands, 870 mi (1,400 km) at the closest point of Mili Atoll, and the Japanese-controlled Northern Mariana Islands, 2,700 mi (4,300 km) from Howland.

Crash-and-sink theory

Many researchers believe that Earhart and Noonan ran out of fuel while searching for Howland Island, ditched at sea, and died. The plane would have carried enough fuel to reach Howland with some extra to spare. The extra fuel would cover some contingencies such as headwinds and searching for Howland. The plane could fly a compass course toward Howland through the night. In the morning, the time of apparent sunrise would allow the plane to determine its line of position (a "sun line" that ran 157°–337°). From that line, the plane could determine how much farther it must travel before reaching a parallel sun line that ran through Howland.

At 6:14 AM Itasca time, Earhart estimated they were 200 mi (320 km) away from Howland. As the plane closed with the island, it expected to be in radio contact with Itasca. With the radio contact, the plane should have been able to use radio direction finding (RDF) to head directly for the Itasca and Howland. The plane was not receiving a radio signal from Itasca, so it would have been unable to determine a respective RDF bearing. Although Itasca was receiving HF radio signals from the plane, it did not have HF RDF equipment, so it could not determine a bearing to the plane. Almost no communications were transmitted to the plane. Consequently, the plane was not directed to Howland, and was left on its own with little fuel. Presumably, the plane reached the parallel sun line and started searching for Howland on that line of position.

At 7:42 AM, Earhart reported, "We must be on you, but cannot see you – but gas is running low. Have been unable to reach you by radio. We are flying at 1,000 feet." At 8:43 AM, Earhart reported, "We are on the line 157 337. We will repeat this message. We will repeat this on 6210 kilocycles. Wait." Between Earhart's low-on-fuel message at 7:42 AM and her last confirmed message at 8:43, her signal strength remained consistent, indicating that she never left the immediate Howland area as she ran out of fuel. The U.S. Coast Guard made this determination by tracking her signal strength as she approached the island, noting signal levels from her reports of 200 and 100 miles out. These reports were roughly 30 minutes apart, providing vital ground-speed clues. Based on these facts, and the lack of additional signals from Earhart, the Coast Guard first responders initiating the search concluded that she ran out of fuel somewhere very close to and north of Howland.

During the 1970s, retired USN captain Laurance Safford began a lengthy analysis of the flight. His research included the intricate radio transmission documentation. Safford concluded that the flight had suffered from "poor planning, worse execution".

In 1982, retired USN rear admiral Richard R. Black, who was in administrative charge of the Howland Island airstrip and was present in the radio room on the Itasca, asserted that "the Electra went into the sea about 10 am, July 2, 1937, not far from Howland".

British aviation historian Roy Nesbit interpreted evidence in contemporary accounts and Putnam's correspondence and concluded that Earhart's Electra was not fully fueled at Lae.

William L. Polhemous, the navigator on Ann Pellegreno's 1967 flight that followed Earhart and Noonan's original flight path, studied navigational tables for July 2, 1937, and thought Noonan may have miscalculated the "single line approach" intended to "hit" Howland.

David Jourdan, a former Navy submariner and ocean engineer specializing in deep-sea recoveries, has claimed that any transmissions attributed to Gardner Island were false. Through his company Nauticos, he extensively searched a 1,200-square-mile (3,100 km2) quadrant north and west of Howland Island during two deep-sea sonar expeditions (2002 and 2006, total cost $4.5 million) and found nothing. The search locations were derived from the line of position (157–337) broadcast by Earhart on July 2, 1937. Nevertheless, Elgen Long's interpretations have led Jourdan to conclude, "The analysis of all the data we have – the fuel analysis, the radio calls, other things – tells me she went into the water off Howland."

Earhart's stepson George Palmer Putnam Jr. has been quoted as saying he believes "the plane just ran out of gas".

Earhart biography author Susan Butler posits that the aircraft went into the ocean out of sight of Howland Island and rests on the seafloor at a depth of 17,000 ft (5 km).

Tom D. Crouch, senior curator of the National Air and Space Museum, has said the Electra is "18,000 ft. down" and compares its archaeological significance to the Titanic, saying, "the mystery is part of what keeps us interested. In part, we remember her because she's our favorite missing person."