FLUG REVUE September 2005: HuDs on civil airliners advance

September 2005

HUDS IN AIRLINERS

By Sebastian Steinke

On a spring day in March 2005 thick mist enshrouds the airport of Milan Malpensa. The meteorologists determine the horizontal ground visibility at less than 150 metres. This is less than the minimum range required for take-offs (runway visual range, RVR). Traffic is suspended. Only a Lufthansa CityLine CRJ-200 regional jet is taxiing towards the runway for an on-schedule take-off bound for Germany. That it is able to do so is the result of a technical innovation: the aircraft is equipped with the Rockwell-Collins Head-Up Guidance System (HGS) and hence is allowed for the first time to take off with only 75 metres RVR. 68 European airports have approved the equipment and allow such take-offs.

Despite the mist, the captain has no difficulty making out the runway axis, using an additional electronic directional marker which is reflected directly in his field of view and appears razor-sharp in bright green on a fold-down, small screen. When it comes to landing, the HGS once again proves invaluable. Although the Canadair jet is not equipped for automatic landings by autopilot in poor weather, the display's virtual needles in his field of view enable the captain to safely recognise and manually aim for the runway under instrument approach conditions up to 200 metres RVR.

The very last moments of the approach, at which the pilot has to decide at the minimum altitude whether he can see the clear runway and will proceed to touchdown or whether he will perform a goaround, are also much easier with a HGS. The captain does not have to constantly alternate his gaze between cockpit displays and external view. Moreover, the often simultaneous transition from autopilot to manual control of setdown is also easier.

With 43 HGS-equipped CRJ200's and 20 CRJ700's, Lufthansa (LH) is one of the first airlines to pioneer the HGS on its regional jets and is now considering whether to equip the 15 A380's it has ordered with optional head-up displays (HUD). As airline pilot Ingo Tegtmeyer, Lufthansa's A380 project pilot and head of A340/A330 operations, told FLUG REVUE in an interview at Lufthansa's Frankfurt base, “A HUD can significantly stabilise visual approaches.” Experience gained by the US airline, Delta Air Lines, which has equipped its 737-800 fleet with HUDs, suggests that in visual flight pilots regularly hit the touchdown zone more accurately with a HUD than without.

On the other hand, this active long-haul pilot believes that because the A380's redundant autopilots have been certified as failsafe, the megaliner can fly automated landings under CAT III without needing any HUD. It is therefore partly a price issue as to whether Lufthansa will order the additional HUD electronics which, although welcome, are not absolutely essential in the A380, or at least prepare the way for a later retrofit by including the necessary wiring. Here we talking about a 6 digit sum per aircraft. No later than two years before the planned Lufthansa deliveries, which are still officially scheduled to commence in mid-September 2007, Tegtmeyer will have to have specified the cockpit configuration for Lufthansa's A380's. Then the first four A380's, registrations D-AIMA to D-AIMD, will join the 2008 summer flight schedule with Lufthansa's crane emblem on their tails. The later resale value of the jets on the second-hand market is already an issue today, as is a policy of cost containment. As Tegtmeyer points out, “The basic question is always, 'How can I improve safety and economy?'”

Two other airlines, FedEx and Air France, have already decided to buy the Thales digital A380 system (D-HUD). Lufthansa captain Tegtmeyer explains that FedEx is already planning strategically for its HUDs to be equipped later on with enhanced vision system (EVS). This entails an infrared camera in the nose recording bright live television imagery even at night-time and in poor visibility, which can be shown to the pilot in his axis of vision over the HUD. Qantas is also interested in this technology, including on the A330, so as to ensure that CAT I approaches, which are normal on the fifth continent, are allowed even in poor weather. Air France on the other hand has had positive experience with the HUD on some Airbuses it inherited from Air Inter.

Head-up displays originate from the practice of aiming with the crosshairs in military aircraft, but already in the Second World War this was replaced by more accurate optical systems with semi-opaque mirrors. A lot of airline pilots in the USA are former military pilots accustomed to flying with a HUD who persuaded their new employers of the virtues of HUDs in civilian aircraft. That is why, according to Tegtmeyer, US airlines are especially open-minded about the possibility of adding a HUD. European pilots on the other hand were mostly trained for commercial aircraft from the start, according to Tegtmeyer, and are not automatically thrilled at the thought of having a HUD.

Head-up displays are particularly easy to integrate into modern glass cockpits. The data they require is already processed in digital form and only has to be transferred to another black box by databus. However, it is important that too much information should not now land in the pilot's field of view and disturb or distract him. “Clutter” i.e. overloaded displays, are the main drawback of HUD technology. Tegtmeyer: “We don't want the entire primary flight display with all its associated information presented all over again in the HUD. If the HUD displays too much information it loses its advantages.”

The latest generation of the Thales D-HUD is therefore restricted in the core to presenting an artificial horizon with altimeter and variometer on the right, speedometer on the left and heading indicator at the bottom. Depending on the particular phase of the flight, the display may automatically change its content and HUD on A340

warn of specific dangers. These include TCAS warnings of imminent collisions with other aircraft and avoidance recommendations, TAWS ground-collision warnings (“Pull up” display) and windshear warnings (“Wind shear” display). EVS data from the infrared camera and also the virtual, three-dimensional terrain reliefs of future synthetic vision systems can be integrated later on.

The HUD-overlaid field of view of the flightdeck transparency is 35 degrees wide and 26 degrees high, as seen by the pilot. The Thales display for the first time receives its data from a light, power-saving liquid-crystal projector unit and no longer from a CRT. The image in the SXGA standard achieves a resolution of 1280 x 1024 pixels with a maximum brightness of 10,000 candela per square metre. That is up to 40 times as bright as a notebook display. On the A380, the data is transmitted via the AFDX databus, but in the future it could be supplied by the A429 bus on the A320 and A340 family and transmitted to the slide projector from the HUD control unit by optical fibre.

Since 13 April 2005, Airbus has been trying a D-HUDS unit in the A340-600 and plans to have the system certified by the end of 2006 as a primary flight system. All the other fly-by-wire aircraft built by Airbus, including the A400M, are expected to follow. Meanwhile Boeing is not sitting back idly either: when the final cockpit configuration of the 787 is unveiled at the end of August, two head-up displays will belong to the standard serial production fit.

From page 34 of FLUG REVUE 9/2005

Last updated 18 August 2005

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