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Secondary domain



The ability to complete approaches in low visibility/ceiling conditions is improved for aircraft equipped with some combination of navigation derived from augmented GNSS or ILS and other cockpit-based technologies or combinations of cockpit-based technologies and ground infrastructure. OI 107117 low Visibility/ Ceiling Approach Operations

Guided Visual Approach concepts have been successfully demonstrated and implemented at SEATAC. These involve using the aircraft autoflight RNAV capabilities (letting the aircraft fly the approach) despite being “Cleared for Visual Approach to Runway XX” by the Tower. The resulting flight track is much more accurate than hand-flying a traditional visual approach.

Head-up Guidance Systems (HGS) are more and more prevalent on state-of-the-art aircraft such as the Bombardier C-Series, Boeing 787, and Airbus A-350. The pioneer for this technology was Alaska Airlines with their fleet of 737s. HGS permits precision flight path guidance, energy management and increased safety. The pilot views critical flight data on the transparent combiner in the forward field of view. The pilot’s vision is out of the cockpit, focused at infinity, not captured by head-down activity.

Key basic features of the HGS include recovery guidance in the event of unusual occurrences (TCAS alerts, unusual attitudes, windshear), flare guidance during all approaches, and low visibility takeoff and approach guidance.

Potential hazard

Failure to recognize the need for and to execute a missed approach when appropriate is a major cause of approach and landing accidents.

More than 70% of approach-and-landing accidents contained elements which should have been recognized by the crew as improper and which should have prompted a go-around.

It is also observed than when an unstable approach warrants a go-around decision, less than 20% of flightcrews actually initiate a go-around.

Unstabilized and rushed approaches contribute to approach and landing accidents.

Continuing an unstabilized approach is a causal factor in 4% of all approach and landing accidents.

Approximately 70% of rushed and unstable approaches involve an incorrect management of the descent-and-approach profile and/or energy level (i.e., being slow and/or low, being fast and/or high).

The risk of approach and landing accident is higher in operations conducted in low light and/or visibility, on wet or otherwise contaminated runways, and with the presence of optical or physiological illusions.

More than 70% of CFIT and runway excursion/overrun events occur:

In low visibility;

In hilly or mountainous terrain;

On contaminated runway; and/or,

Under adverse wind conditions.

The lack of acquisition or the loss of visual references is the most common primary causal factor in approach-and-landing accidents.

Corroborating sources and comments

Airbus Flight Operations Briefing Notes, Approach and Landing, FSF ALAR Task Force Conclusions and Recommendations;

Guided Visual Approach PowerPoint

20121030 Guided Visual Approach DCP DRAFT PDF

ATC clears an aircraft for an RNAV-­‐TF/RNP-­‐RF/RF or TF to ILS or any instrument approach, and when the aircraft breaks out of the clouds and sees the airport or the preceding aircraft on the same path, then ATC may clear the aircraft for a “Guided Visual Approach.”

The aircraft must remain on the IAP LNAV/VNAV track guidance, under visual flight conditions.

There is still considerable disagreement for a standard phraseology needed to implement GVA.

Currently being demonstrated at SEATAC with notable success.

Head-up Guidance Systems

December 2013:

Honeywell announces a “Combined Vision System” that merges Enhanced Vision Systems (EVS – based on forward-looking sensors) with Synthetic Vision Systems (SVS – that rely on GPS-based aircraft position with respect to a terrain database). This merged capability could offer the safety and situational awareness benefits of both systems. By combining the benefits of both EVS and SVS, the FAA might offer even more “credit” to pursue lower landing minimums. Terrain representations using the on-board database have been seamlessly integrated with the “out the window” view from the EVS camera and can be displayed on the Primary Flight Display (PFD) together with navigational information.

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