The Federal Aviation Administration is quietly and deliberately ushering in a new era of "Superman vision" to the cockpits of corporate and airline industry cockpits.
Rather than seeing through walls (or clothing), the superior vision is unveiling airports, increasing safety and access to runways cloaked by low ceilings or fog while decreasing costs via an "aircraft-centric" philosophy.
The sea-change in instrument weather operations is largely germinating from two FAA-sanctioned working groups under RTCA's special committee 213, enhanced flight vision systems (EFVS) and synthetic vision systems (SVS). The groups are working in parallel with European industry and regulators.
The basic thrust of SC-213, which was established in 2006, is to see how emerging vision technologies, whether computer-based synthetic vision systems (SVS), sensor-based enhanced flight vision systems, or a combination of the two, can augment or replace a pilot's natural vision to allow for safer low-visibility instrument approach and runway operations that today require expensive ground and aircraft instrumentation and training. Typically business aviation equips with such upgrades first, followed by commercial airlines.
Innovations in cockpit technology could bring an era of 'superman vision'
Through such aircraft-centric "equivalent visual operations", the FAA hopes to ultimately provide uniform airport throughput and safer operations independent of the weather. For operators, having the approved equipment and procedures on board is likely to mean assured access into airports that are sometimes unreachable today in certain weather conditions.
The group's "products" are used by the FAA to develop advisory circulars or other guidance material as well as flight and operational rules. For industry, the structured approach provides assurance of FAA buy-in when it is time to build the hardware. "You don't have to build it and worry that they're not going to approve it," says one member of the committee.
SC-213's SVS committee (Working Group One) most recently completed a set of performance standards for using SVS in lieu of natural vision to reduce the usual 200ft (60m) "decision height" for a Category I instrument landing system approach down to 150ft.
If the pilot does not see the runway environment using natural vision at the decision height, the aircraft must abandon the approach. The standards are hardware agnostic and do not specify whether the display of information is to be heads-up or heads-down.
Rockwell Collins is firmly established as a head-up display provider for airlines and business aviation and is investing heavily in SVS-on-HUD technologies, most recently introducing a low-cost HUD for lower end business aviation cockpits. Competitor Honeywell meanwhile is focusing most intently on head-down display of SVS that may be augmented by real-time forward-looking sensors. Honeywell and Universal Avionics have both certificated HDD synthetic vision systems for Part 25 business jets, but to date the upgrade serves as an enhancement to situational awareness, not as credit for lower landing minima. Honeywell's SVS in the Gulfstream PlaneView cockpit is now flying in more than 200 aircraft, according to Gulfstream.
© John Croft
The SVS benefits could begin to multiply if the FAA approves the SVS group's 150ft plan this summer, allowing manufacturers to then ask the agency for approval for the SVS-aided approach credit. While the needed SVS technology already exists, the missing ingredient is a full flight-test programme to prove out the concept.
"The long-lead item is the flight evaluations within industry, and for the FAA to determine that the operation is safe and can be completed within the bounds of the safety analysis, and whether it can be done head-up or head-down," says Sarah Barber, principal systems engineer of advanced concepts for Rockwell Collins and a member of SC-213 Working Group One.
"There would have to be some level of certification approval because there are additional functions required than what's normally required for an ILS," says Barber. Those functions include monitors for deviation from the approach path and the integrity of the GPS-based SVS datastream.
Barber says Working Group 1 had initially had pushed for 100ft minima with SVS, but backed off to 150ft as a first step as that altitude meshed well with an existing FAA special authorisation that allows operators with certain head-up displays and Category II instrument approach training to descend to 150ft on a Category I approach with a minimum (RVR) of at least 1,400ft.
A typical Category I approach requires an RVR of 1,800-2,400ft. Category II approaches have a 100ft decision height and 1,200ft minimum . The difference with SVS however will ideally be that operators will not need the additional training or higher performance HUD, saving money and training time for the equivalent safety and access to airports.
Barber says flight testing of SVS on a HUD completed by Rockwell Collins in March showed that flight technical error (how well a pilot can control the aircraft to the commands from the navigation computer) was lower using a HUD than an HDD, which could potentially translate to a lower requirement for operators equipped with a HUD.
Ultimately, Rockwell Collins hopes SVS landing credit could be extended down to 100ft, or equivalent to the decision height that is granted to specially trained pilots and aircraft equipped with infrared-based enhanced flight vision systems today. Enhanced flight vision typically comprises an infrared sensor for real-time video imagery and a HUD to display the enhanced forward view as well as aircraft navigation and performance information.
"We think that with SVS alone we should be able to get to a 100ft decision height," says Barber. "What we're hoping is that flying the SVS image with the ILS becomes so intuitive and low workload for the pilot, that you could do 100ft [minima] without recurrent Category II ILS training."
While SC-213's EFVS contingent (Working Group 2) has been ushering in lower minima in stepwise fashion, its next move is by far the most headline grabbing: an architecture that will allow for pilots to substitute EFVS for natural vision all the way from the approach to the gate, providing there is at least 300ft RVR available. The group plans to finish the work by year's end or early 2012, after which the FAA will in theory change the various documents to allow the practice for operators that can meet the standards.
A preliminary version of the architecture calls for a two-pilot crew trained in EFVS operations, each equipped with a HUD, and with the pilot-not-flying monitoring the equivalent visual segment to verify correct aircraft approach trajectory and being able to assume control and continue to safely operate the aircraft if there is a problem.
The EFVS, projected on the HUD, must provide the primary visual references by which the pilot manoeuvres the aircraft from decision height through touchdown and roll-out and taxi to the ramp and gate area, or to taxi out to the runway for take-off.
The aircraft-centric capability would remove the need for certain airport infrastructure, including centreline and touchdown lights and three sets of transmissometers (touchdown, mid-field and roll-out) as opposed to one.
At present, the group is proposing a fail operational architecture that would allow the approach to continue with certain failures. It is not clear what type of sensor will be required to give pilots sufficient situational awareness in 300RVR conditions, although in theory a millimetre wave radar system combined with an infrared sensor may suffice. EFVS typically use cooled infrared sensors operating in the near-IR and midwave bands.
Gulfstream has the most systems flying (more than 500) with Bombardier and Dassault progressively adding EFVS certifications to their lines. An operator approved for EFVS operations can use the vision system on the HUD in lieu of natural vision down to a 100ft decision height.
An intermediate step toward 300RVR will be the expected approval by the FAA this summer of SC-213-prompted rule changes to allow for any appropriately equipped and trained EFVS operator to land with an RVR of 1,000ft, an approval FedEx Express and NetJets received via an exemption from the FAA in 2009.
REPORTING RUNWAY VISUAL RANGE
Airports generally report runway visual range information - an instrumentally derived value that represents the horizontal distance a pilot can see down the runway - using one of two instruments - a transmissometer or a forward scatter meter (pictured).
A transmissometer measures the "transmittance" of the atmosphere over a baseline distance while a forward scatter meter measures the extinction coefficient of the atmosphere. In either case, the RVR value is calculated based on input from the sensors as well as measurements ambient light conditions and runway light intensity "based on the expected detection sensitivity of the pilot's eye", according to the Federal Meteorological Handbook.
The device must be located within 150m (500ft) of the runway centreline and within 300m of the landing threshold.