Below is a typical short “feet wet” flight for a P-3 (seven hours) – LAJES FIELD, The Azores (run by the US Air Force) to Royal Netherlands Naval Air Station VALKENBURG [The P-3 can fly for twelve hours. Add a four hour preflight and tactical briefing and a two hour post flight debrief and you have a pretty long day. Repeat every 18 hours for a month when there is a submarine “flap” going on and you get some idea of what the life is like.]
The flight is shown below. On 29 May 1986, my crew and I flew Navy P-3B TACNAVMOD aircraft Bureau Number 153433. The Minuteman on the vertical stabilizer is the official logo of PATROL SQUADRON 92, based from 1970 to 1993 at NAS SOUTH WEYMOUTH, MA, and at NAS BRUNSWICK, ME, from 1993 until its recent decommissioning earlier this year. The TACNAVMOD designation (Tactical Navigation Modification) indicates that the airplane’s tactical and navigation systems were upgraded in 1984.
The Nav Log shows the standard Navy format. Each leg is preflighted with the trusty old E-6B computer known to every private pilot, a plotter, and a set of dividers. The log shows that we expected to do a little over four-and-a-half hours of “real” navigation before we got close enough to Holland for the pilots to play navigator with the TACAN and DME. We started engines at 0117 Z and took-off at 0131 Z. At 0206, traveling at a TAS of 347 knots and a ground speed of 349 knots, we lost our TACAN lock as we went further out to sea.
The P-3B TACNAVMOD carried three electronic nav systems plus a sextant, driftmeter, and an ancient LORAN-C that required the use a hand crank to match sine waves on a small, green CRT screen.
This was a huge improvement over the earlier P-3B and P-3A, which carried a sextant, driftmeter, LORAN-A, and three electronic systems that never worked: the ASN-42 inertial nav, the ASA-47 airmass computer, and the Drift Computer. Aboard one of these earlier airplanes I usually watched in dismay as, after takeoff, all three of the darn things merrily went off in different directions, leaving the navigator sweaty and unhappy.
Mission Commander's Station
The TACNAVMOD was far superior, carrying three systems you see noted on the nav log. “XN” refers to the Litton ASN-72 Inertial Navigator, and a great piece of gear it was, too. “DA” refers to the Doppler Airmass computer, which used a Doppler beam to calculate drift and plug it into true heading and true airspeed to get a second electronic track. The Greek Omega symbol referred to the Omega Navigation System, a set of ground stations broadcasting on very low frequency to provide fixing information. The TACNAVMOD navigator tracked all three systems and then kept track of where they were in regard to his dead reckoning track to see what was what. You’ll note that in the log all three kept pretty well together. Because a flight never is as preflighted, each HEAD entry is a new heading given to the pilot to correct for wind change, magnetic variation change, and electronic system drift. Of the three, the XN was the most accurate despite its being a DR position and thus not usable as a fix source.
OMEGA was a fix source but not as accurate as XN. DA was the least dependable in part because it was the oldest and because the Doppler beam hitting the water and bouncing back would periodically lose its lock and the NAV would see the red “OH CRAP” lite illuminate, indicating that DA was taking a nap. On this flight it seems to have worked pretty well. At 25,000 feet the driftmeter was useless, plus in order to use it you had to depressurize the airplane, push it out through the right side of the fuselage, and squint down over it to line-up the wave white caps with the reticule.
Because all three nav systems were working I did not have to use the sextant, a blessing because to use the sextant the NAV has to stand on his seat with his left leg, put his right knee on the back of the SENSOR THREE operator’s seat, brace his left elbow against the overhead ventilation well, and hold the sextant with his right hand trying to keep the celestial body inside the littler spirit bubble as the airplane bounces along.
Part of every flight was the Nav Systems Check. The form reproduced here shows that I checked the NAV systems against the Pilots’ FLIGHT nav systems, such that there was a less than three degree discrepancy among the Inertial, Doppler, and Airmass Computers, Heading Systems Indicators (HIS), Aircraft Heading Reference System (AHRS), Wet Compass, Double Directional Indicator (DDI), Calibrated Air Speed Indicator, Altimeters, MB-9 manual true airspeed computer, Outside Air Temperature Indicators, Automatic True Airspeed Computer, and the magnetic variation shown on the chart (why we needed a four hour preflight is becoming clearer, no?)
The chart tracks what the Nav Log shows. All three electronic systems worked well, with the OMEGA plot starting to drift away from XN and DA as we neared land and FLIGHT picked-up TACAN at VALKENBURG. The multi-colored lines on the chart are LORAN lines – segments of huge circles of equal signal delay from several different LORAN-C stations – the same system you use if you have an M-1 or GLN-88 in your own plane. Each can be used to plot one line of bearing. (I used the same chart to and from Holland, so the plots with arrows to the North show the flight to, and arrows pointed South show the return flight.)
Our time in Holland wound-up to be brief, to say the least. We had a preflight for the return trip to LAJES scheduled for 20 hours after we landed at VALKENBURG. So, being Navy fliers with an image to uphold, we did the logical thing: we hopped a bus to go sight-seeing. Three hours later we balls of fire all fell asleep on the canal ferry, simply tuckered out. We did revive in time to see some of Amsterdam’s fabled night life, grabbed some Zs, and then the next day returned to The Azores. Navy life!
Modern systems like GPS have changed everything about how people navigate these days. But I wouldn’t feel as secure using GPS to find Holland as I did aboard the Navy’s P-3Bs.