20-Sep-2002 -- A Flight to the N22º W159º Confluence
On September 20, 2002, Todd Hammons and I flew to the Hawaiian Island of Kaua'i [kau (w)ah' ee]* and the confluence at N22º W159º. Our aircraft was a single engine Cessna Cardinal (Tail Number: N30599) owned by Moore Aviation. Our flight plan had us departing Honolulu [hoh' noh loo' loo] International Airport at 1:45 pm. The route was initially northeast, but after clearing the controlled airspace surrounding Honolulu and the temporarily restricted airspace over Pearl Harbor, we headed to the Kahe [kah heh] Power Plant on O'ahu's [oh ah' hoo] western shore. The island of Kauai was 70 nautical miles (nmi) to the northwest and the visibility between the islands was 20 to 25 miles. When we notified Honolulu Radio that we were passing the Mid channel reporting point, we could see nothing but ocean in all directions.
Twenty minutes later, we came to the coastline of southern Kaua'i. From there, we began a clockwise tour around the island. As we passed east of Pacific Missile Range Facility (PMRF) Barking Sands, we could see the island of Niihau [Nee ee hau'] to the southwest. The Nâ Pali [NAH' pah lee]
Coast lies along the northern shore of Kaua`i. The sun was bright and the clouds were few
as we passed this land of vertical cliffs, tall mountains, difficult terrain, and beautiful scenery.
On the east side of the island, the weather changed to light rain, low clouds, and a visibility
of 7 or 8 miles.
After landing and refueling at Lîhu`e [LEE’ hoo eh] airport, we departed and set our course for the confluence at N22º W159º. The N22º W159º confluence is located along the 073º radial, 18.96 nmi east of the Lîhu`e Very high frequency Omni Range (VOR) transmitter (See COMMENTS ON NAVIGATION below). The transmitter uses a radio frequency of 113.5 MHz and is located at the Lîhu`e airport. We flew directly from Lîhu`e airport to the confluence on the 073º radial at an altitude of 2500 ft. When the aircraft's Distance Measuring Equipment (DME) showed that we were 19.0 nmi from Lîhu`e, we entered a right hand holding pattern having one minute legs and an inbound heading of 253º on the compass. After completing two circuits of the pattern, we switched to a right hand holding pattern having an inbound heading of 73º. After our fourth passage through the confluence, we returned to Honolulu via the Mid channel reporting point and the Kahe Power Plant - landing at 5:45 pm.
Even without the Aerial Disqualification clause (FAQ #1.7), this trip counts only as an attempted visit. At 19 nmi from Lîhu`e airport, the positioning error of the VOR/DME navigation system is potentially 2500 m. This does not meet the Project’s positioning error requirement of 100 m (FAQ #3.2). The scene to be photographed was mostly of white clouds and light blue ocean (Kaua`i was not visible during our attempt due to the weather). To maintain contrast on our instrument panel, the outside scene was washed out. In addition, the resolution of the panel from our disposable film camera was not sufficient for reading the indications of the instruments. The various indications shown at the bottom of the"Confluence Navigation" picture were documented at the time the pictures were taken and are artificial illustrations of the actual displays shown in the four instrument panel images. Since the pictures from the confluence do not show the island of Kaua`i, comparing them with future visits will only provide information about the changes in weather near the confluence. A clear day with visibility greater than 25 miles is needed if future visits are to photograph the island. Another interesting fact is that the ocean depth at the confluence is approximately 1600 fathoms (9600 ft).
COMMENTS ON NAVIGATION
The plane did not have a GPS receiver, but it was equipped with a radio-navigation (NAV) device called a VOR receiver. It was also equipped with DME. Pilots monitor the VOR receiver display -- called a course deviation indicator (CDI) -- to verify that their position lies along a desired radial line of direction from the VOR transmitter on the ground. DME transmitters are collocated with most VOR transmitters and broadcast signals that aircraft receivers can use to calculate the distance to the transmitter. The DME receiver in our aircraft displays the distance to the ground transmitter in nautical miles. Its typical accuracy is 3% of the distance being measured or 900 m, whichever is greater. At 19 nmi, the DME accuracy is approximately 1100 m. On the other hand, a calibrated VOR can have an angular direction error of +/- 4 degrees. A 4-degree radial error at a distance of 19 nmi is equivalent to a 2500 m error in position.
Describing the procedure for determining the aircraft's radial line of direction with respect to a VOR transmitter can help explain the CDI images shown the "Confluence Navigation" picture. In these images, a direction of travel is selected by rotating the compass dial on the CDI until the desired direction of travel is at the top of the display. If the aircraft is on the VOR radial indicated by the desired direction of travel, the vertical needle in the middle portion of the CDI will be centered and a FROM (FR) flag will be visible in the lower left quadrant of the display. This means that if the aircraft flew in desired direction of travel, it will fly "away from" the VOR. If the aircraft is on a radial that is 180º opposed to the the desired direction of travel, the needle will also be centered but a TO flag will be visible on the display. This indicates that if the aircraft flew in the desired direction of travel, it will fly "to" the VOR.
*Hawaiian Pronunciation Note: ‘au’ [ow] is a diphthong formed from two vowels ‘a’ [ah] and ‘u’ [oo]. More information on the Hawaiian language and its pronunciation can be found at the website: www.hawaiianlanguage.com.