Pilot and crew.
So far we have referred to "the pilot", but of course the vast majority of air transport operations are carried out with a minimum crew of two pilots. It is a fundamental purpose of Standard Operating Procedures (SOPs) to coordinate the activities of the two pilots to achieve the safest possible operation.
By the mid-1970s, the number accidents to jet airliners was causing serious concern, with many of those on approach and landing occurring during attempts to land with poor visual cues. These all occurred using procedures where the PNF was expected to make a call-out "at" DH indicating what cues he or she had seen.
Normally both crew members are strongly motivated to bring the flight to a successful landing, and in marginal conditions the PNF is also aware that it is the PF's actual responsibility to decide if the cues are sufficient. Consequently there is a strong tendency for the PNF to report ANY visual cues that he or she sees, especially if specific items such as "approach lights" have been stated as being the minimum necessary for descent below DH.
The motivation to make a callout.
It is improbable that any First Officer will decide that something seen should NOT be called out, although it may not actually fulfil the requirements of "adequate visual reference". Doing so would be to pre-empt the Captain's decision. But in the most marginal conditions, the USAF trials noted that after seeing limited cues and making sighting calls, there is an extremely strong impulse for the PNF to maintain a head-up view, to continue to verify the changing cues. This strong impulse directly conflicts with the usual procedural requirement, which is that the PNF should immediately return to monitoring instruments when below DH.
The common result is that the aircraft actually continues below DH with the PNF incapable of being an effective monitor of the flight path, while the PF is attempting to make his or her determination of the aircraft position and rate of change of position. In other words, the aircraft descends below DH with the pilot at the controls not necessarily having adequate information for flight path control, while because of the unrealistic nature of his or her "procedural" obligation, the pilot monitoring is unable to detect deviations from a safe path, because he or she is looking at the same inadequate information.
A recent "both heads up" accident.
This is exactly what the NTSB decsribed in its causal factors or the 2013 Birmingham A300 crash, which allude to [the First Officer's] "distraction from her pilot monitoring duties by looking out the window when her primary responsibility was to monitor the instruments", while "the captain was also responsible for managing the approach in its final stages using a divided visual scan ...... and his distraction from his pilot flying duties by looking out the window likely contributed to his failure to adequately monitor the approach."
In 1976, the US National Transportation Safety Board made a special study of the subject, and the NASA Human Factors specialists based at the Ames facility started making extensive evaluations, including large scale flight simulator exercises with US airline crews to look at both the physiological issues and the organisation of crew tasks.
NTSB Special Study.
The NTSB study made a number of specific recommendations in regard to crew coordination procedures for visual transition. They should
- ensure continuous (unbroken) monitoring of the aircraft's instruments from the OM to landing.
- provide specific wording to announce when each crew member is relinquishing previously assigned duties or responsibilities, if an exchange of visual scanning responsibilities is required, .
- Limit sighting callouts to cues associated with the runway environment, and prohibit any which could result in the premature abandonment of instrument procedures.
To overcome the problems discussed here, many operators started to use the "Pilot Monitored Approach" (also known as just "monitored approach", "split duty" approach, "Pilot-in-charge Monitored Approach" [PicMA] etc. crew coordination distribution of duties, which fully complies with the NTSB study recommendations.
Using this procedure, during an instrument approach the pilot-in-charge ("P1"), who will be making the actual landing (normally the Captain) carries out the function of Pilot Monitoring with the standard Pilot Not Flying (PNF) duties and callouts. The other pilot (second pilot or co-pilot, normally the First Officer) "P2" is assigned responsibility for immediate aircraft control as Pilot Flying (PF) for the approach, using the autopilot if available.
As the aircraft approaches Decision Height the P1 increasingly devotes his attention to assessing visual cues, while the P2 makes required callouts.
On arrival at Decision Height the P2 calls "Decide". This signals to the P1 very clearly that "time is up", and a decision is needed. A "Decide" call is far more imperative than simply calling "minimums": that is really just advice that an altitude has been reached, and is more easily ignored, especially if delegated to an automated callout system.
In response to the "Decide" call, the P1 announces his decision according to his assessment of those visual cues, with either "Land" or "Go-around" (or equivalent phraseology).
If the call is "Land" this triggers a change of task: the P1 assumes control and continues to make the landing, while the P2 continues to monitor the instruments and acts as PNF during the landing.
If the P1's decision is "Go-around", the P2 immediately starts to go-around while the P1 reverts to instrument references and continues as PNF throughout.
If visual reference is subsequently lost after a "Land" decision, or other conditions necessitate that the landing be abandoned (a rejected landing), the P1 continues the subsequent go-around as PF.
This has numerous advantages compared to procedures in which the P1 or PF flies the approach to either landing or go-around with no change of control.
- Overall command capability and situational awareness is enhanced. As the P1 is relieved of the immediate short-term control workload, he or she can assess any changes in the environment, e.g. updated weather reports or runway occupancy information from ATC, which are communicated directly to him/her
- Premature transfer to misleading visual cues is minimised. In a "traditional" approach, the PNF is often required to make "sighting" calls of the approach lights or runway environment, triggering the PF to start attempting his transition to visual cues while simultaneously flying the aircraft. These cues may or may not adequate for control. With the "monitored approach" procedure the P1 is under no obligation to control the aircraft until DH is reached and sufficient visual cues have been confirmed
- Unbroken monitoring of instruments can be assured: it is the principal task of the P2. In any variable conditions, visual cues are by definition inconsistent and may deteriorate as well as improve. With traditional procedures, if the PM has called out sight of some visual cues, the PF must start his/her own assessment of them. In the event that the PF is not satisfied he or she must resume instrument flying (which requires a finite re-adjustment time) and then detect and correct any instrument flight errors which have built up in the interim.
No break in instrument monitoring.
When using traditional PF/PM procedures in such conditions, the PM is expected to make a call-out "at" DH indicating what cues he or she has seen. There is a strong impulse for the PM attempting to make "sighting calls" to maintain a head-up view of the changing cues, and not immediately return to monitoring instruments as is usually required.
For this reason most knowledgeable authorities recommend that the flight path be maintain on instruments alone to as low an altitude as is possible, and callouts that could lead to premature transition to external cues be prohibited. Procedures which require an exchange of instrument monitoring and external cues acquisition tasks should clearly set out calls to coordinate such task exchanges, which is extremely difficult to achieve. When using PicMA procedures, PMA only one pilot attempts to make this transition, and such callouts are eliminated, making for a much simpler procedure"Land or Go-around" Decision-making is optimised by three principal factors.
- The P1 can be "head-up" for the maximum possible time, assessing the aircraft position and velocity in relation to the visual cues as they develop.
- The P1's workload is reduced by not having simultaneous responsibility for the instrument flight path, so the time actually needed to reach a decision is reduced.
- The P1 is forcefully reminded by the P2's "decide" call to terminate visual assessment at the correct point.
1) and 2) together combine to produce the best decisions in the worst visual conditions: maximum assessment time and minimum decision-making time. This will achieve a higher Approach Success Rate and minimises the possibility of unnecessary go-arounds and possible diversions with their attendant economic and safety implications. 3) minimises the probability of continued descent below DH without a decision actually being made.
It is worth noting that in Canada, a 2006 Advisory Circular 0239 describes the "Pilot Monitored Approach" procedure, noting that "Proper use of the PMA permits the left seat pilot to improve the safety related to making the decision to transition from instrument conditions to visual conditions for the landing.
During a PMA the left seat pilot has significantly more "heads-up" time for visual scanning outside the flight deck. This extra time permits the pilot conducting the landing to determine whether sufficient visual references exist to judge the position and rate of change of position of the aeroplane in order to decide to continue the approach visually to a safe landing."
In recognition of this, 2006 Advisory Circular 0237 indicates that operators using the PMA procedure may be permitted to commence approaches with a lower approach ban RVR.
In a Continued approach to landing, the P2's unbroken and continuous sight of the instruments enhances his ability to make for example altitude, speed and vertical rate callouts as necessary.
In a Go-around at DH: if a go-around is required it is carried out by the P2 who is already completely attuned to instrument flying and "primed" for the go-around. This enhances the accuracy of the go-around and minimises the risk of infringing Obstacle Clearance by inadvertently descending below Decision Height before initiating the go-around.
Recommendations.
The ICAO - Federal Aviation Administration - Flight Safety Foundation joint Controlled Flight Into Terrain Education and Training Guide, recommended to all operators by the FAA, is quite unambiguous. In section 2.1.6, it notes that most CFIT accidents occur during approaches in IMC and at night, and recommends that operators consider adopting PicMA for these approaches.