trimmed automatically for maximum efficiency,

reducing the need to constantly toy with the throttle levers, which has a tendency to wear out the engines more quickly. DEECS and other generic devices such as Engine Monitoring System (EMS), also record engine performance in fine detail. This information can be downloaded by engine specialists for diagnosis after the aircraft returns from its sortie (or during ground-runs, if required), permitting them to fine-tune the powerplants and be forewarned of possible impending component failures. Older engines require the attention of a ground crewman's well-tuned ear to help isolate faults. Smell and hearing feature as strongly as visual cues, even through the barrier of ear protectors which actually tend to filter the noise down such that oddities (clanking, grinding, etc) become more apparent.

The big engines turn small generators mounted at the front of each engine, or attached to the side of the casing, capable of producing massive reserves of power. Second only to its high-pressure electro-mechanical hydraulic system, an aircraft's electrical system, fed around literally tens of miles' worth of voltage-regulated conduits, drive all the big power-guzzling electrical systems: radar, countermeasures, electro-hydraulics, and so forth. At this stage the buffer's ancillary electrical lead may be disconnected too, and the fighter becomes a free agent, with engines turning over nicely and the displays and key electronics warming up.

The engines also provide hydraulic power by pressurizing the whole flight control nervous system, and this accounts for the drooped posture of an inactive jet fighter. Compressed air piped from the engines is used also for cabin pressure, to inflate the crews' g-suit bladders during high dynamic flight loads, and (on board emerging designs such as Eurofighter 2000) to supply breathing air to the pilot, by means of a molecular sieve which furnishes oxygen with a purity of up to 95 per cent.

With hydraulics working, at the DCC's initiation the pilot flexes the bird's feathers, checking all the control surfaces are working satisfactorily: rudder, élevons, spoilers, flaps, slats and so on are all given a thorough workout, with the ground crew presiding at key vantage points. This includes normal control movements of the stick and rudder, verification of augmentation systems, normal flap and slat operation, and proper trim - establishing the controls near the normal neutral point, via a trim button on the control stick which can be teased up, down, left and right. By definition, loss of engine power customarily results in creeping loss of other control power, and this is why deadstick (engines out) emergency landings are such a hairy procedure.

Powerhouse of the koder fighter: its engines. Pilots' hearts start palpitating if these go awry inflight! The bullet fairings on these J79-GE-17s house the electrical generators which provide the aircraft's operational power - eveiything depends on them.

(Ken Mackintosh)

Electronics check-out mostly falls within the navigator's job description. This is also conducted as part of the general Power On agenda. One of the first tasks is to align the inertial navigation set (INS), a crucial piece of equipment fitted to every self-respecting fighter. Older categories of INS, such as the Litton LN.12 used on most land-based F-4s, employ accelerometers and gyros which sense movement about the three axis (up/down, left/right and forwards). With the assistance of a navigation computer, they process these movements into meaningful information in the form of present position latitude/longitude coordinates which are constantly updated from the moment the aircraft's wheels began to turn. The displays generated by these Litton devices were known as 'windows' and presented the information on spinning counters, similar to a car's odometer. Gyro-compass alignment of these now obsolete systems with current position (the parking spot coordinates and its elevation) took up to 15 minutes on a cold day, and in-flight drift tended to be in the order of miles for every hour of flight-time, necessitating constant updates. They were also prone to in-flight 'dumping' (going awry), which necessitated in-flight realignment and updating, all over again.

Transistor number-crunching of the inputs provided by the electrical signals generated by the cogs and pulleys contained in the INS, a technology introduced in the late 1960s, witnessed the introduction of light-emitting diode (LED) digital displays, similar to those found on domestic

radio-By modern standards, an antiquated navigation display, using old-fashioned counters. In the 1960s such INS readouts were relatively cosmic. Compare this with ... (Ferranti)

. . . the two MFDs and central CRT found in the cockpit of the F-117A stealth fighter. Note also the tiger-striped ejection seat handles and (at top right) one of the fold-down sunshades, which is held in place by Velcm! (Lockheed)

LAUNCH 41

alarm clocks, but accuracy remained just as shaky until the advent of the solid-state ring-laser-gyro (RLG) INS a decade later, tied in with microchip number-crunching to compute the required information, which is now customarily displayed on an MFD in alphanumerics. Errors still are introduced, but system reliability in terms of both accuracy and mean time between failure (MTBF) is greatly improved. For example, F-15E crews praise their Honeywell RLGs highly: 'The thing is a rock. It aligns in 4 minutes, stays where it's supposed to in flight, then winds up with one knot or less of ground speed and within 100 ft of your parking place - every time.' At the time of writing, work on newer, even more sensitive digital quartz inertial (DQI) 'tuning fork' electrical gyros is underway. DQI INS systems will offer inexpensive throwaway technology (that is, if it goes wrong, it is cheaper to bin it rather than repair it), and in miniaturized forms these are also being developed for new smart weapons. It will take some time yet for this to percolate down into operational use.

To the uninitiated, it begs the question, why all this fuss over a system that can be prone to unreliability?!

Updated, the INS is vital in helping to slave radar and E-0 sensors to stored target or offset coordinates which are crucial for reasonably accurate blind or smart bombing. It is critical in assisting with navigation over vast expanses of nothingness such as ice-caps and oceans (or a truly black night), where there exist no visual identifying features to help follow the flight-plan even in conjunction with a moving or electronic map display, an all-weather eye such as radar, or night-time E-O sensors. It can be slaved to the navigation computer and an autopilot in some instances for virtually hands-off point-to-point flight, a vital asset in speedy low-level flight. And it is autonomous - i.e. it does not rely on outside sources, as do radio navigation aids, which are relatively easy for the enemy to jam. It thus serves to assist with surprise attack. Moreover, many modern fighters' air-to-air weapons and weapons-aiming systems are equally reliant on inertial reference inputs in order to work properly. INS can help narrow the area of choice or target parameters when identifying these with various sensors or weapons seekers - of crucial assistance in the time-compressed, exacting nature of military aviation, especially at low-level.

Navigation computers are also programmed by the

The back of the F-14 Tomcat is stuffed with circuit-breaker panels, fairly typical of a modern fighter and reflecting its enormous quantities of electrical systems. (Grumman)

back-seater during the Power On phase of pre-flight checks and preparations. At the top of the market, navigators use the DTMs, which stuff the brains of the navigation computers with all the pertinent mission data in a time span of 8-30 seconds. Such technology also features nowadays on relatively humble fighters, such as New Zealand's digitally updated A-4K Skyhawks. In intermediate technologies, such as the Lear-Siegler ARN-lOl(V) DMAS equipping the F-4G Advanced Wild Weasel, the DTM would provide only basics such as tanker ARCPs, information pertaining to established bull's-eyes, and the coordinates of diversionary airfields which might be called-up in the event of an emergency. In this instance, the specifics regarding the various legs of the mission must be tapped into the navigation keyboard one at a time, in sequence, correctly keyed with the proper prefix letters, 'D' (data point) or T' (turn point), such being crucial in the automatic activation of sensors on board reconnaissance jets, in particular.

In yet older analogue systems (the RAAF F-1 IIC's pre-AUP Bomb-Nav-System being a prime example), navigation legs are entered one at a time, as the flight progresses, based on a checklist or computer print-out listing all the relevant information, carried into the cockpit by the navigator alongside his other flight paraphernalia. This can be a taxing task for single-seaters using commensurate technology, such as the A-7P flown by the Force Aérea Portuguesa.

And much of this technology still is prevalent owing to the widespread market for refurbished hand-me-down fighters.

Diagnostics of the primary equipment, using built-in test (BIT) features, is also performed on such crucial equipment as the radar, or Big Eye, and E-O sensors, this being undertaken by the multi-fingered,

multi-toed wizzos. It may comprise simply checking the whole gamut of electrical circuits. On more modern, digital aircraft this often involves running a programme of checks; on older technology, actually switching through all the knob settings, one at a time, and ensuring that all is working satisfactorily, and in extremis, having a nose for the gear. Until very recently, before microchips came of age and valves and similar high-voltage, heavy-duty electronic components prevailed, many navigators ascertained the health of their equipment by smell ! For example, a nauseous odour might indicate a short-circuit, or imminent failure of some component. Even today, equipment can be prone to overheating so has to be tweaked.

Such subtleties have largely been replaced by the computerized self-diagnostic MFD readouts common today, which even pilots in multi-crew types call-up and consign to the computers' 'bins' with surprising ease (such is the MTBF reliability of modern avionics, and the extent of their all-singing, all-dancing cautionary alerts). Most crews run through these checks in automaton fashion, as they are so well-rehearsed.

With regard to electrical current, in both ancient and modern systems, major electrical circuits are protected by copious banks of circuit-breakers. A power surge (such as that generated during powering-up) might cause some to pop (out), and normal service can be resumed by pressing them back in place again.

If they keep popping, then something is genuinely wrong with the circuitry. This might result in a sortie

stand-down, or some head-scratching by ground crew followed by the insertion of a freshly serviced line-replaceable unit (LRU: a black box which can be readily uncoupled and replaced by a serviceable unit in only a few minutes).

With all the displays working as advertised, the BIT and other checklists complete, the Crew Chief gives the aircraft a final visual examination, mostly checking for obvious problems such as fuel or hydraulic leaks. Some of these leaks must be viewed in relative terms. All fighters (including stealth designs) feature numerous drain holes in their bellies to prevent an explosive build-up of fuel or hydraulic liquids, and it takes only a small amount to smear the underside of a modern jet fighter with their characteristic stains - ugly, but necessary.