Sabena's avionics upgrade is providing a service extension for Belgium's Lockheed Martin C-130s.
Harry Hopkins/ANTWERP
OF THE 2,000 LOCKHEED C-130 variants manufactured, more than half were built before 1970. It is not surprising, therefore, to find that the Belgian air force's problem is a common one: what to do with early C-130 transports.
Six years ago, Belgium decided to keep its 12 vintage C-130Hs in service until 2010-15. In a life-extension programme, completed in 1993, the aircraft's outer wing was replaced, and older avionics renewed as required. Something more fundamental was needed if the aircraft were to last the distance, however, and an integrated vehicle and mission management system (IVMMS), based on existing Honeywell units, was proposed by airline-maintenance contractor Sabena Technics.
The programme was driven, by the increasing flexibility of digital equipment, as well as the growing maintenance problems associated with analogue equipment and electromechanical flight instruments. Being a completely new avionics system, rather than one of "added-on" components, initial testing extended over a year, up until May 1996. Flight International has "flown" the simulator (and observed an operational flight) to compare the old and the new.
COCKPIT CHANGES
The flight engineer's position and engine instruments are unaltered. Although few navigators have been trained recently, the navigation station is kept, and partially re-equipped, for some tactical missions. Other evident changes include the installation of an electronic flight-instrument system (EFIS) - incorporating a Rockwell-Collins Primus 710 weather radar display; an automatic-pilot system, with a glareshield-mounted navigation control panel and two mission-control and display units (CDUs) ahead of the engine controls.
The EFIS are small, because of space limitations. Their cathode-ray tubes slope down behind the instrument panel (presenting the screens at an ideal angle to the eye). The standby horizon is set at a higher level, with standby airspeed-indicator and altimeter added.
The electronic attitude-display indicator has an altimeter scale on the right, with 500ft (150m) and 1,000ft intervals clearly marked by wedges. A speed scale on the left shows all reference airspeeds - a great advance on the single-needled, tightly scaled, instrument flown in the simulator. The electronic horizontal-situation indicator (EHSI) has the vertical speed-scale to its right - a slightly unusual placing, but well within normal eye scan.
The navigation control panel (NCP) of the Honeywell Category II dual digital autopilot (identical to that of the C-130J) is an improvement on the rudimentary original controls, which were located on the centre console. Selector knobs for heading and azimuth reference were in a difficult location near the flight-control trim switches behind the engine-lever quadrant. The NCP interferes with forward view far less than the radar screen previously on top of the glareshield.
DATA CONTROL
The engine-condition levers are angled left, away from the right CDU forward of the engine lever quadrant. They still intrude, so it is easier for the co-pilot to programme his with his right hand. A McDonnell Douglas MD-11 pilot would recognise the CDU format, but many of the 14 mode keys have different functions - among which are the tuning-selection mode keys, now the primary access for the manual selection of radio communications and navigation frequencies, so eliminating radio-control heads.
The CDUs could show abnormal and emergency drills, but CDU activity - in avionics and mission management - is too great for this. For the same reason, manually or automatically selected frequencies are separately shown on two liquid-crystal displays, outboard of each electronic attitude-display indicator. These so-called flightdeck displays (FDDs), carry cipher buttons, for voice-secure activation - and play a role in air drops. The CDUs show post-flight equipment status and history.
At the navigation station are a third EHSI - slaved to the co-pilot's - and a third CDU (with an awkward vertical keyboard), for redundancy and occasional operational use. The mission plan can be loaded here, through a data-transfer unit (DTU). The IVMMS can read from, or write to, the DTU's solid-state memory.
Mission-data upload cartridges can also be used to download flight data, for analysis on a personal-computer-based mission-planning ground station. Honeywell software presents, selective menus for mission preparation, including radio pre-sets and air-drop or search routines; a modem interfaces with the Jeppesen MEMRYCORD flight-planning network.
IN FLIGHT
The flight demonstrated one particular capability of the IVMMS - the computed air-release point (CARP). The C-130 was loaded with six 1,500kg drop-packs of sand. The inertial-navigation-system (INS) alignment process is protected against aircraft movement - always likely during loading, because it goes automatically to navigation mode, and warns of degraded navigation, by bell and CDU message. The INS will recapture later against global-positioning-system (GPS) position.
At flight-management-system (FMS) initiation, GPS present position can be inserted via the CDU scratchpad. The database format - in grid format (such as 31UFS 6274 6426) is accurate to 3m. A route was built manually, via the right CDU, with CARP path interposed between two way points - together with drop-load details.
The CDU's take-off page computes torque and reference speeds; default conditions are 50% flap, serviceable nosewheel-steering and full anti-skid braking. Runway-braking action is entered as a two-digit reference, and a drag index takes account of aircraft configuration - such as paint finish and underwing fuel tanks.
For our demonstration flight, after clearing controlled airspace north-west of Brussels Zavantem Airport at 8,000ft, we continued at 1,000ft and 225kt (415km/h) under autopilot control to a military drop-zone. Nominal descent is on a 4.7° slope at 2,000ft/m (10m/s) - depending on weight and cargo location. The autopilot vertical-navigation mode is still under development (cruise altitude, speed and fuel flow are selected from the performance manual). Climb mode will have to be flexible, not based simply on optimum performance.
Tall masts and chimneys near Antwerp skimmed by; the need for precise navigation at low altitude in instrument flight conditions clearly demands GPS satellite signals of military accuracy.
On entering the CARP phase, its CDU page was reviewed. Drop-site co-ordinates, release altitude and speed were already determined; but temperature and wind velocity at drop altitude and at target must be brought up to date, to adjust load fall velocity and drift.
The load exit time (4.5s) was determined by the number and type of pallets; the time to reach a free-descent state (3.5s) on the type of parachute. These times come from a ballistic database. At 140kt ground- -speed, the drop would take 28s, and spread along 700m; the path flown allowed for an airborne drift of 700m on 100í, from pallet release to ground impact.
EHSI screen size and minimum scale are not ideal for presenting drop patterns. An instrument landing system (ILS) localiser-type display of the final drop path appears at CARP initial point, or lateral intercept on a repeat run; one-dot deviation is 1°, or a 50m offset at the drop point. Even at low airspeed, the display could be flown manually and corrected comfortably. Autopilot tracking will be cleared for a blind drop; but final approval is subject to stringent trials of trim control (as were early Cat III landings in civil operations).
The aircraft was slowed below 150kt, with 100% flap (rapid tactical slowdown is pre-planned at 10kt per 0.5km). With the rear fuselage door raised and with the ramp level, flaps were returned to 50% with a 2.5° nose-up attitude at 140kt. A preliminary run was made, with abort and downwind-positioning path pre-planned. Nearing the drop site - elevation 115ft - altitude steadied at 800ft and the CARP path commenced.
Final configuration is with flaps raised to 20% - giving 8° angle of attack at 128kt. Weight must be accurately checked, as each 600kg is worth 1kt of reference speed. The whole load was now held back by one rear-retaining strap - ready to eject under its own weight at this body attitude. In case of a hang-up, full flap is immediately selected, to return to a flat attitude, and the fuselage door lowered to block the exit.
As the green drop light illuminated, the loadmaster operated a simple guillotine on this strap, by a line running back from the front. In a few seconds, the load was gone and the flaps again extended for manoeuvring. A perfectly straight line of pallets spread only a few metres north of the marked line, with each green parachute fanned out downwind.
An FMS-only approach was then made to a military airfield. The in-service decision height, is 400ft, but 200ft was demonstrated on a 3° slope, although 7° is possible. Guidance in centreline and glidepath is "cone shaped", as on an ILS. GPS and the database's high-definition grid ensures ILS-type accuracy. Civil GPS, without differential enhancement and positions, entered in latitude/longitude, might be 100m in error. On the final ILS approach at Brussels, localiser and glideslope indications on the left coincided with FMS guidance on the right.
REASONS TO UPGRADE
Military aircraft, which fly fewer hours than civil types but in more challenging environments, are commonly subject to mid-life updates. The most important element, in major upgrades today, is avionics improving ownership costs and mission capability. The capital cost, of the Sabena/Honeywell upgrade - just over $3 million an aircraft - is modest, and, as it also has some compatibility with the C-130J programme, it reduces cross-fleet differences from new C-130Js.
Working on two aircraft at a time, the contract finishes in 1998. Three can be worked on in the Sabena Technics layout, with space for four. Foreign customers often want local work-offsets, but Sabena prefers to do the first conversion at Brussels, to deal with peculiarities in aircraft configuration, and the learning curve of customer's engineers. US C-130 maintenance specialist Evergreen is acting as industrial partner under a memorandum of understanding.
Source: Flight International
