Visual References

Visual References

Description

The phrase 'Required Visual Reference' is used in relation to the transition from control of an aircraft by reference to flight deck instrumentation to control by reference to external visual references alone. Those visual references, including aids, should have been in view for sufficient time for the pilot to have made an assessment of the aircraft position and rate of change of position in relation to the desired flight path. In Category III operations with a decision height the required visual reference is that specified for the particular procedure and operation. (ICAO Annex 6, and PANS-ATM).

The establishment of visual references at the completion of an instrument approach is an important process which determines whether the approach may be continued to landing, or a go-around must be flown.

   Note: the vertical or slant view of the ground through broken clouds or fog patches does not constitute an adequate visual reference to conduct a visual approach or to continue an approach below the applicable MDA/H or DA/H.

The section below headed "European Regulations" details what these visual references must be. The remainder of this article deals with the process of transition within the aircraft cockpit.

According to Flight Safety Foundation (FSF) Approach-and-landing Accident Reduction (ALAR) Briefing Note 7.3 — Visual References , "The transition from instrument references to external visual references is an important element of any type of instrument approach."

The briefing note points out that two common Task task-sharing philosophies are common:

  • "Pilot flying-pilot not flying (PF-PNF) task-sharing with differences about the acquisition of visual references, depending on the type of approach and on the use of automation:
    • Nonprecision and Category (CAT) I instrument landing system (ILS) approaches; or,
    • CAT II/CAT III ILS approaches (the captain usually is the PF, and only an automatic approach and landing is considered); and,
  • "Captain-first officer (CAPT-FO) task-sharing, which usually is referred to as a shared approach, monitored approach or delegated-handling approach.

"Differences in the philosophies include:

  • The transition to flying by visual references; and,
  • Using and monitoring the autopilot."

"The task-sharing for the acquisition of visual references and for the monitoring of the flight path and aircraft systems varies, depending on:

  • The type of approach; and,
  • The level of automation being used:
    • Hand-flying (using the Flight Director [FD]); or,
    • Autopilot (AP) monitoring (single or dual AP)."

The briefing note than proceeds to discuss task sharing and other considerations for different types of approach.

European Regulations

AMC1 to IR-OPS CAT.OP.MPA.305(e) and Appendix 1 to EU-OPS 1.430 define the required visual references for continuion of a precision approach or a non-precision approach as follows:

Non-Precision Approach A pilot may not continue an approach below MDA/H unless at least one of the following visual references for the intended runway is distinctly visible and identifiable to the pilot:

(i) Elements of the approach light system;

(ii) The threshold;

(iii) The threshold markings;

(iv) The threshold lights;

(v) The threshold identification lights;

(vi) The visual glide slope indicator;

(vii) The touchdown zone or touchdown zone markings;

(viii) The touchdown zone lights;

(ix) Runway edge lights; or

(x) Other visual references accepted by the Authority.

Precision Approach A pilot may not continue an approach below the Category I decision height ... unless at least one of the following visual references for the intended runway is distinctly visible and identifiable to the pilot:

(i) Elements of the approach light system;

(ii) The threshold;

(iii) The threshold markings;

(iv) The threshold lights;

(v) The threshold identification lights;

(vi) The visual glide slope indicator;

(vii) The touchdown zone or touchdown zone markings;

(viii) The touchdown zone lights; or

(ix) Runway edge lights.

Category II Operations A pilot may not continue an approach below the Category II decision height ... unless visual reference containing a segment of at least 3 consecutive lights being the centre line of the approach lights, or touchdown zone lights, or runway centre line lights, or runway edge lights, or a combination of these is attained and can be maintained. This visual reference must include a lateral element of the ground pattern, i.e. an approach lighting crossbar or the landing threshold or a barette of the touchdown zone lighting.

Category IIIA Operations For Category IIIA operations, and for Category IIIB operations with failpassive flight control systems, a pilot may not continue an approach below the decision height ... unless a visual reference containing a segment of at least 3 consecutive lights being the centreline of the approach lights, or touchdown zone lights, or runway centreline lights, or runway edge lights, or a combination of these is attained and can be maintained.

Category IIIB Operations For Category IIIB operations with fail-operational flight control systems using a decision height a pilot may not continue an approach below the Decision Height ... unless a visual reference containing at least one centreline light is attained and can be maintained.

Accidents and Incidents

The following events on SKYbrary involve lack of visual reference as a factor:

On 23 May 2022, an Airbus A320 came extremely close to collision with terrain as the crew commenced a go around they did not obtain any visual reference during a RNP approach at Paris CDG for which they were using baro-VNAV reference to fly to VNAV/LNAV minima. The corresponding ILS was out of service. The Investigation has not yet completely established the context for the event but this has been confirmed to include the use of an incorrect QNH which resulted in the approach being continued significantly below the procedure MDA. Six Interim Safety Recommendations have been issued.

On 14 October 2019, a Sikorsky S92A manoeuvring below low cloud in poor daylight visibility in an unsuccessful attempt to locate the intended private landing site flew north towards rising ground approximately ¾ mile east of it, coming within a recorded 28 feet above terrain near to occupied houses before making an emergency climb and over-torqing the engines followed by an unstable but successful second approach. The Investigation found relevant operator procedures absent or ineffective, an intention by the management pilot in command to reach the landing site despite conditions and uncertainty about the applicable regulatory context for the flight. 

On 29 January 2015, a Boeing 737-800 crew attempting to fly an NDB approach to Bergerac, with prior awareness that it would be necessary because of pre-notified ILS and DME unavailability, descended below 800 feet agl in IMC until an almost 1000 feet per minute descent when still over 8 nm from the runway threshold triggered an EGPWS ‘TERRAIN PULL UP’ warning and the simultaneous initiation of a go-around. The Investigation found that the PF First Officer was unfamiliar with NDB approaches but had not advised the Captain which resulted in confusion and loss of situational awareness by both pilots.

On 27 February 2016, an Airbus A320 making an into-sun visual approach to Jaipur in hazy conditions lined up on a road parallel to the intended landing runway and continued descent until an EGPWS ‘TOO LOW TERRAIN’ Alert occurred at 200 feet agl upon which a go-around was initiated. The Investigation found that although the First Officer had gained visual reference with both road and runway at 500 feet agl, the Captain had seen only the road and continued asking the First Officer to continue descent towards it despite the First Officer’s attempts to alert him to his error.

On 9 July 2018, an ATR 72-600 continued a non-precision approach to Al Hoceima below the procedure MDA without obtaining visual reference and subsequently struck the sea surface twice, both times with a vertical acceleration exceeding structural limits before successfully climbing away and diverting to Nador having reported a bird strike. The Investigation attributed the accident to the Captain’s repeated violation of operating procedures which included another descent below MDA without visual reference the same day and the intentional deactivation of the EGPWS without valid cause. There was significant fuselage structure and landing gear damage but no occupant injuries.

On 15 September 2012, the crew of a Beech Super King Air on a medevac flight making an ILS approach to runway 23 at Glasgow became temporarily distracted by the consequences of a mis-selection made in an unfamiliar variant of their aircraft type and a rapid descent of more than 1000 feet below the 3500 feet cleared altitude towards terrain in IMC at night followed. An EGPWS PULL UP Warning and ATC MSAW activation resulted before the aircraft was recovered back to 3500 feet and the remainder of the flight was uneventful.

On 15 March 2012, a Royal Norwegian Air Force C130J-30 Hercules en route on a positioning transport flight from northern Norway to northern Sweden crossed the border, descended into uncontrolled airspace below MSA and entered IMC. Shortly after levelling at FL 070, it flew into the side of a 6608 foot high mountain. The Investigation concluded that although the direct cause was the actions of the crew, Air Force procedures supporting the operation were deficient. It also found that the ATC service provided had been contrary to regulations and attributed this to inadequate controller training.

On 24 February 2004, a Cessna 550 inbound to Cagliari at night requested and was approved for a visual approach without crew awareness of the surrounding terrain. It was subsequently destroyed by terrain impact and a resultant fire during descent and all occupants were killed. The Investigation concluded that the accident was the consequence of the way the crew conducted the flight in the absence of adequate visual references and with the possibility of a black hole effect. It was also noted that the aircraft was not fitted, nor required to be fitted, with TAWS.

On 12 May 2010, an Afriqiyah Airways Airbus A330 making a daylight go around from a non precision approach at Tripoli which had been discontinued after visual reference was not obtained at MDA did not sustain the initially established IMC climb and, following flight crew control inputs attributed to the effects of somatogravic illusion and poor CRM, descended rapidly into the ground with a high vertical and forward speed, The aircraft was destroyed by impact forces and the consequent fire and all but one of the 104 occupants were killed.

On 13 April 2013, a Lion Air Boeing 737-800 flew a day non precision approach to runway 09 at Bali (Denpasar) and continued when the required visual reference was lost below MDA. Despite continued absence of visual reference, the approach was continued until the EGPWS annunciation 'TWENTY', when the aircraft commander called a go around. Almost immediately, the aircraft hit the sea surface to the right of the undershoot area and broke up. All 108 occupants were rescued with only four sustaining serious injury. The Investigation attributed the accident entirely to the actions and inactions of the two pilots.

Related Articles

Further Reading

  • ICAO Doc 4444: PANS-ATM;

Flight Safety Foundation

The Flight Safety Foundation ALAR Toolkit provides useful training information and guides to best practice. Copies of the FSF ALAR Toolkit may be ordered from the Flight Safety Foundation ALAR website

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