Category: Applications

There I was, well above Angels 40, sound asleep wearing a positive pressure oxygen mask and helmet with the droning of multiple jet engines in the background for company. Then, I was abruptly awoken by an aircrew member urgently calling my name.

On waking I noticed that it was colder and darker than I remembered when I had nodded off. The only light was that strange ambient light you only experience at high altitudes, and there was zero radio chatter in my helmet headset.

When I reached the cockpit, I noticed the ambient light again because the radar screens were blank, as were all the electronic screens for our multiple sensors, and then it dawned on me. There had been some kind of an electrical failure. I glanced at the navigation displays to determine our position, and to my dismay, discovered they were all blank and lifeless as well. This should not have been, as all navigation and emergency avionics instruments had extensive battery backups.

Then I looked closer and noticed that not only were the screens blank, but the inertial power switches were in the standby position. All kinds of thoughts raced through my mind as the pilot-in-command, easily 20 years my senior (we will call him Bill for brevity) explained that after the fifth and last over-water air refueling things were progressing nominally — until they weren’t. Suddenly, amber and yellow caution lights appeared, followed quickly by red warning lights, all of which warned of imminent power failures of the jet-engine-driven generators. The special mission aircraft we were flying had enormous generators on all engines, so large they precluded thrust reversers on any of the engines. The aircraft needed all that power to function as a mission aircraft, but fortunately needed no electrical power to remain airborne.

We completed the “total loss of electrical power” checklist, and for the time being all was well. The copilot calculated the aircraft could fly for another 10+ hours with IFR reserves using the fuel on board, and from our high altitude could “glide” with engines at idle for a couple hundred miles. So, no worries right?, as one of our Australian exchange pilots liked to say. Of course, there were several worries, the main one being no one knew exactly where we were. Like Daniel Boone we were not officially lost, just a bit bewildered.

Airborne Class

Another aircrew instructor and I were onboard this particular aircraft enroute to what must remain an undisclosed location down under, to teach a class and develop a curriculum on overwater navigation for crews flying reconnaissance aircraft. My apologies for the brevity, but that is all I am allowed to say about the aircraft and our mission to this day.

The aircraft had every bell and whistle you can imagine and then some, but it was essentially an electric aircraft as far as mission and navigation were concerned, and at the moment we were fresh out of that commodity. My instructor colleague and I were about to give out first impromptu overwater navigation class at altitude. We were not yet in extremis, but if we did not do everything exactly right, it might be everyone’s last overwater navigation class.

Back to Basics by Necessity

I had one of my flight bags with basic navigation gear with me on the flight deck and not stowed in the cargo hold, which was not accessible in flight. In that bag I had protractors, rulers, various conversion tables including the critical Aeronautical Almanac and Sight Reduction Tables for Air Navigation, plus an antique but serviceable sextant. The sextant needed to be treated with kid gloves, which is why I had the bag with me rather than stowed in the baggage compartment.

My colleague and I suggested that as an augmented crew, we run through the emergency checklist for total loss of electrical power once again. Then we reviewed the Dash One (aircraft bible) on electrical failures and recommended actions plus all the flight crew actions 30 minutes prior to the power failure. We checked circuit breakers throughout the aircraft including in the mission compartment, the avionics and the mission equipment bays. We found nothing amiss except a plethora of red warning lights that told us nothing new; we were literally in the dark.

The good news was that aerodynamically the aircraft was performing perfectly. Considerable experience with the persnickety nature of emergencies and aircraft electrical systems precluded making any drastic changes. The autopilot was off and the aircrew was hand-flying the aircraft that, when perfectly trimmed, actually required very little effort. That was good, since under even the best scenario we were “feet wet” — over water for at least another seven hours.

Just before the massive electrical failure, the navigator calculated the aircraft was passing the “go-no-go equidistant” point of flight, which on long overwater flights means the aircraft, under nominal conditions and considering the prevailing wind and drift, could proceed to the landing destination but no longer had fuel or endurance to return to a suitable airport nearest the original “feet wet” departure point. In other words, we only had enough fuel to continue to our destination and could not turn around and return to another suitable airport to land. Plus, deviating from our scheduled route and flight plan without being able to notify the flight-following stations meant that if we ditched, no one would be looking for us in the right location. Additionally, politically the number of foreign airports where we could land our type of reconnaissance aircraft were few and far between. We elected to proceed to our original destination.

This was not a democratic process or decision, as the pilot-in-command always has the last say. He is ultimately responsible for the aircraft and crew. But we were all in the same predicament, so after we had each voiced our opinions, the aircraft commander made the correct decision to proceed and to change the aircraft configuration as minimally as possible. This meant we would not try to bring the generators back online until we were over land and within gliding distance of a suitable airport, which by our best guess was seven hours distant.

The aircraft had a RAT,  or ram air turbine, for just such emergencies, except that it was not for this emergency. RATs are typically used for short durations, generating power to make emergency radio calls. Once deployed, a RAT could not reliably be re-stowed, and there was no record of anyone having deployed a RAT for more than seven hours. Plus, it would probably affect the handling of the aircraft. No one knew exactly how nor how much drag it would produce, and how it would affect our endurance or emergency glide capabilities. Best to leave the RAT stowed for now. If the engine generators and bus did not come back online once we were over or near land, then we would consider deploying it and making emergency radio contact. While being out of radio contact was not unusual for our type of aircraft, the FAA and its equivalent at our destination would probably be the agencies initially concerned. As a last resort, our parachutes all had survival radios that could be utilized for communications on guard channel — presuming someone was monitoring guard and heard our call.

Older Is Not Necessarily Better

We were straight and level on a heading for our destination, determined from the original flight plan and from weather and atmospheric data more than 48 hours old. We needed real-time or as close to zero age of data as we could manage, and it would have to be generated internally.

The aircrew was a senior crew, but rarely flew over water out of sight of land or out of range of electronic navigation aids. The aircrew was, to put it politely, on average nearly twice the age of my colleague and I, who were qualified overwater aircrew instructors. The aircraft commander was still ultimately in charge, but his comment or charge to us was, “OK guys, you’re the experts, now what?”

Status Quo

As far as arriving at our destination, if the engines continued to run and we continued on this course, without encountering or having to deviate blindly around significant weather, we would eventually make land fall feet dry. We would then hopefully extend the RAT, make radio contact, and explain our predicament to ground control or the country’s Air Defense fighters scrambled to intercept us for violating their Air Defense Identification Zone (ADIZ) without the proper radio calls. This is where the handheld radios in our parachutes would come in handy, explaining on guard channel to the fighter/interceptor pilots that we were allies and good guys and just experiencing a communications failure. All of which would be embarrassing and potentially fraught with dangerous consequences, but which could be avoided if the power miraculously came back on or if we followed the emergency “communication out” ADIZ penetration procedures for that particular country.

These emergency procedures, while almost global in nature, were well known in theory but rarely, if ever, practiced by flight crews. They consisted of: flying within a prescribed 10-mile wide corridor, arriving at the ADIZ penetration point on course and on time, and then flying a specific triangular pattern for three consecutive iterations, while listening on guard, if possible, and then proceeding to our original destination as planned, possibly still “comm out,” flying a communications out, VFR (visual) approach and landing as planned. Such an arrival might create a minor stir, but we would be seen as obeying the international flight rules and hopefully no one would be chastised or court-martialed.

Do We Have a What?

To accurately fly the ADIZ penetration procedures, we needed to know where we were, how fast we were flying (our groundspeed), and what factors were affecting our flight planned heading. Since it was still daylight, our best bet was to use “back to basics” navigation techniques to determine our groundspeed, and then as the stars appeared, we could better determine our position and refine our heading.

The crew regarded me with some skepticism as they realized I intended to use an old-fashioned sextant to determine the speed and heading and then navigate a multi-hundred-million-dollar modern reconnaissance aircraft. An aircraft with multiple Doppler receivers, inertial navigators, pinpoint radars, satellite communications, racks for a GPS receiver that had yet to be installed and an avionics suite that was second to none at the time. I proposed we navigate for seven hours with an obviously antique handheld brass sextant that I pulled carefully out of a velvet pouch stowed in my flight bag. And I would have done just that, if I had not realized that this aircraft also had a sextant port when the flight engineer mumbled something about a dusty old sextant case being strapped down in the avionics bay.

Within minutes, the old sextant case was opened to reveal a pristine sextant still wrapped in depot preservatives. It may have literally never been used since it was put on the aircraft, probably as a safety afterthought. Certainly no one on the crew had ever used one on this aircraft, and the senior navigator had not used one since navigator school at Mather Air Force Base in California. Since there was no electrical power, we were not sure the sextant would work or if the displays would be readable. After checking it over, we pushed it through the sextant port and were rewarded with a good pressure seal. We found a spare D-cell battery to power the sextant in emergency mode, hooked up that cable and were in business. General Curtis LeMay would have been proud.

Non-Traditional Navigation Sensors

For those of you not familiar with celestial navigation, or using a sextant with the accompanying Air Almanac Star Reduction Tables (remember, the Sun is a star) basically it goes something like this:

“Celestial navigation is the ancient art and science of position fixing that enables a navigator to navigate without relying on dead reckoning, to determine their position. Celestial navigation uses ‘sights,’ which are angular measurements taken between a celestial body and the visible or artificial horizon. The sun is most commonly used, but navigators also use the moon, a planet or one of 57 other navigational stars whose coordinates are tabulated in the Nautical and Air Almanac.

“Celestial navigation sights locate one’s position on or above the Earth. At a given time, any celestial body is located directly over one point on the Earth’s surface. The latitude and longitude of that point is known as the celestial body’s geographic position (GP) or sub-point, which can be determined from tables in the Air Almanac.

“The measured angle between the celestial body and the visible or artificial horizon is directly related to the distance between the celestial body’s GP or sub-point and the observer’s position. After some computational sight reductions, this measurement is used to plot a line of position (LOP) on a navigational chart, the observer’s position being somewhere on that line. Most navigators use sights of three to five stars and plot the resulting LOP(s) to minimize the chance for error.”

To begin the process, we needed to know time as exactly as possible, the date where we were located, our altitude and, if possible, an approximation of our location and direction of flight. All that information is provide by crewmember timepieces and basic navigation instruments that don’t rely on electrical power. You enter the tables and complete the pre-computation worksheet with the derived data, which you dial manually into the collimators of the sextant. Then with our bubble sextant representing the horizon, you place the Sun in the middle of the bubble and collimate on it for two minutes, read the resulting number off the sextant, convert it to a distance from the celestial bodies’ known sub-point, and that is your LOP. Since we were traveling in a southwesterly direction, the Sun provided a speed or velocity LOP. It would not determine our location with any certainty, but would provide a reliable estimation of our speed over the Earth.

We knew our basic air speed from the onboard instruments that were still working, but we needed to know our ground speed, which is affected by head, tail or cross winds. Two such Sun sightings over a period of 10 minutes multiplied by 6 gave us our ground speed, and when compared to our airspeed told us that we had a 40-knot tailwind, likely due to a forecast large low-pressure system behind us. Consequently, we would be drifting to the left, which would cause us to steer right a few degrees of our intended course, since the planned tail wind was only 20 knots, not 40. Now we knew our groundspeed and refined our ETA (estimated time of arrival) at the ADIZ penetration point. We conducted Sun shots and calculations every 30 minutes until the Sun set and the stars were visible. Shooting and plotting multiple stars for positions is just a bit more complicated and time consuming, but because it results in an actual position, rather than a speed line, it is much more valuable.

We had additional sources of data as well, which surprised the senior crew — whom we were essentially instructing in the basics of emergency overwater navigation. We plotted the best dead-reckoning line of position based on the flight plan and last known position. Then we plotted several more lines of position based on temperature, ground speed and pressure readings. This is a technique rarely used by navigators today, but one that helps you double-check your assumptions and flight planning data. In the Northern Hemisphere, a low pressure system behind you when heading southwesterly will nominally result in a tailwind and drift to the left of your course, based on the old mnemonic high up right and low down left, just as longitude and latitude mathematical values are based on the mnemonic East is least (minus) and West is best (plus). Similarly, if the temperature is rising over time, then you are most likely drifting to the right. If it decreases, you are likely drifting to the left. Lows are typically cooler than highs. If the barometric pressure is rising, then you are drifting right, and if it lowers, then you are drifting left. These are not all hard and fast rules — you can be on the backside of a major weather system and experience all these phenomenon — but if you are not being tossed about in the middle of a major thunderstorm, these mnemonics can save your life.

Normally a navigator will take one sextant shot per hour while averaging wind, pressure and temperature data over the same time. Given our dire circumstances, we calculated pre-comps and shot planets and stars continuously, on the average of three sights per hour, and took temperature and pressure readings every 10 minutes for the next 7 hours. Arriving at the ADIZ penetration point, we flew our three triangular patterns and were shortly thereafter intercepted by a Canberra aircraft that was conveniently in the area (it turns out our hosts had been expecting us and determined from the radio silence that something was amiss). The Canberra pilot informed us on guard channel (those wonderful parachute radios proved a godsend) that he would lead us to our destination. Thankfully, the weather was VFR (visual flight rules). We followed him down on a visual approach to our destination, and when he broke off in the pattern, we landed uneventfully.

We attempted to bring the engine generators online 30 minutes before the predicted ADIZ point without success. However, in the process the battery connections were re-energized and the inertial devices woke up. Because an airborne initialization required more than an hour’s time, we used them as a groundspeed reference only. Frankly, all the warning messages and flashing lights in the otherwise dark cockpit were almost more of a distraction than help.

Debrief

During the mission debrief, the maintenance crews informed us that a faulty sensor and a computer glitch had caused the power problems. Our generators were fine, but the faulty sensor and computer software had combined to shut down all generators.

Lessons Learned

Looking back on this flight many years later, in retrospect I believe we made all the right decisions. We continued to our destination and did not attempt to fix a major problem over water as long as the basic airframe and engines were doing their job. We followed our flight plan, and if we had ditched, we would have hopefully been found along our route of planned flight.

We made use of the instruments and crew-member capabilities on hand. We used a navigation method vetted over literally hundreds of years with the most modern versions of that equipment available. The crew learned how to use basic data almost always available on any aircraft, powered or not, to lay down not one but multiple lines of position.

Today, if the same scenario came about, the basic decisions would be the same, except that crew members would merely pull out their pocket GPS navigation devices, probably mostly iPhones, and using a power-saving battery plan, navigate their way to their destination. The difference is that the data — weather, groundspeed, altitude, heading and ETA, even to various waypoints — would be instantly available, and it would be accurate to within feet and nanoseconds, not miles and minutes. They might even have been able to call ahead.

Inertial Inertia

Contrary to what some in the Defense Department have been saying, the inertial devices onboard would have been just as ineffective if this scenario was repeated today. The critical and operational limiting caveats that most laymen and even some military users miss about individual inertial devices is that they are intrinsically dumb devices that experience drift and bias phenomena that are not always predictable. Inertial units do not know when or where they are until they are told. Even after they are told, if the inertial units lose power without a battery backup, they need to be told time and time again when and where they are. GPS performs this function very well, and together the two systems are almost the perfect navigation combination.

Without an internal clock and coordinate system (chip-scale atomic clocks [CSAC] will work only after they are initialized and told what time it is, a function more often than not performed by GPS today and in the foreseeable future), an inertial device will not show you where you are on a map display or in any discernible or chartable coordinates. An inertial device, while it is superbly equipped to measure movement in every axis, is basically a three-dimensional device. Inertial units detect up from down, left from right, and acceleration or de-acceleration, but they do not detect changes in time or know their starting, way or endpoints in discernible coordinates without being told. So, yes, Mr. Secretary, it would be great to have an inertial that would run for a thousand years, but first you need the miniaturized atomic reference systems, power systems and coordinate determination systems that will run that long as well.

In other words, we need an inertial system that is a system of systems, which today are ideally comprised of CSAC and GPS devices with a laser gyro. In the not too distant future, a cold atom interferometer MEMS (microelectromechanical system) inertial with CSAC and GPS all backed up by eLORAN is probable. That, however, is a story for another time.

Until next time, wax nostalgic — dig out your old sextant and take a sighting. Until then, happy navigating, and remember that GPS is brought to you courtesy of the United States Air Force.