Introduction

1.1. Committee (PLC) presented a paper titled ‘ATCO Duty of Care’ (PLC, ‘ATCO Duty of Care’ paper presented to the International Federation of Air Traffic Control Associations (IFATCA): 56th Annual Conference, Toronto, 2017). The purpose of the paper was to promote discussion about the concept of duty of care and how it applies to air traffic control officers (ATCOs). It was intended to be an introduction to a concept that many have heard of but that can be difficult to define. Of course, while the topic may be interesting to some, without the means to practically apply the concepts, it may remain too abstract.

1.2 For this reason, the paper proposed a number of broad principles that may be useful in determining the standard of care owed by ATCOs and whether or not that standard has been met. These principles were distilled from a selection of case law where duty of care was considered, particularly where it involved air traffic control.

1.3 The purpose of this paper is to build on the concepts presented in last year’s paper, with an emphasis on developing a methodology to apply duty of care principles to specific situations. Applying duty of care principles to scenarios is useful for two reasons. Firstly, it will help test the principles providing an opportunity to further refine them. Secondly, it will provide an opportunity to examine a typical air traffic control scenario from a ‘duty of care’ perspective and propose a methodology to make sound decisions.

1.4 The paper will attempt to apply duty of care principles to the concept of ‘over servicing’. The paper will define over servicing and then examine the concept in the context of providing traffic information to aircraft in class G airspace. The duty of care principles will be applied to this scenario to determine whether or not they can be useful in determining what actions, if any, should be taken.

IFATCA policy

2.1 There is no IFATCA policy relevant to this paper.

Duty of care principles

3.1 It’s important to consider that the purpose of developing these principles is not necessarily to ensure an ATCO can defend themselves if ever prosecuted for negligence. Although this does happen occasionally, it is very unlikely to occur. The primary purpose is to provide a framework for better decision making in scenarios where ATCO duties may be unclear. This will lead to better, safer decision making and ultimately reflect positively on the professionalism of ATCOs.

3.2 Duty of care is an element of negligence. If a person breaches a duty of care owed to another, and damage results, they could be found negligent (U Magnus, ‘Tort law in general’ in Jan M Smits (ed), Elgar Enyclopedia of Comparative Law (Edward Elgar Publishing, 2nd ed, 2012) , p 879). ATCOs owe a duty of care to pilots and their passengers to exercise a standard of care the same as that of a reasonably competent ATCO (Ibid, p 143). They need not possess the highest expert skill, just the ordinary skill of a competent ATCO (Bolam v Friern Hospital Management Committee (1957) 2 All E.R. 142 at 144 in C Shawcross and K Beaumont, Air Law (Butterworths, 4th ed, 1977), p 78).

3.3 Duty of care is a concept that many ATCOs are familiar with but, arguably, few fully appreciate. At best, this may result in ATCOs not being fully aware of their responsibilities to pilots and passengers. At worst, it could result in an ATCO not acting when they should or acting incorrectly in the mistaken belief they are acquitting their duty of care.

3.4 Through an examination of a number of court cases where the ATCO duty of care was considered, last year’s paper proposed three broad questions that may provide guidance for ATCOs to acquit their duty of care. They are:

1. Has the ATCO made reasonable efforts to obtain and maintain information to ensure the safety of aircraft in their area of responsibility?
2. Has the ATCO reasonably acted on information so as to ensure the safety of aircraft in their area of responsibility?
3. Has the ATCO passed to the pilot information that it’s reasonable to assume the pilot will rely on to ensure the safety of their aircraft?

3.5 By applying these principles, the ATCO should be in a better position to act in a manner that is consistent with both established rules and procedures but also to acquit their duty of care.

Provision of ‘advice and information’

One of the objectives of an air traffic service, as defined in Annex 11 to the ICAO Convention on Civil Aviation (‘Chicago Convention’), is to ‘provide advice and information useful for the safe and efficient conduct of flights’ (International Civil Aviation Organisation (ICAO), Convention on Civil Aviation (“Chicago Convention”), 7 December 1944, (1994) 15 U.N.T.S. 295, Annex 11, 2.2). Regulators and air navigation service providers (ANSPs) give effect to this by publishing rules and procedures that ATCOs, amongst others, are required to follow. Theoretically, provided the rules and procedures are followed, the State can ensure aircraft will have all the advice and information useful for the safe and efficient conduct of flight.

4.1 However, the very nature of information provides a lot more scope for ATCOs to use their judgement. It is not as simple as applying a separation standard. Of course, there are rules and procedures to ensure the timely distribution of relevant information, however the breadth of information at the ATCO’s disposal may mean that not all information is capable of being passed to a pilot. Indeed, too much information may be a risk in itself (R Hansman, H Davison, ‘Effect of Shared Information on Pilot/Controller and Controller/Controller Interactions’ in L Bianco et al (ed), New Concepts and Methods in Air Traffic Management (Springer, 2001)). What information should be made available to the ATCO? What should be passed to a pilot? What should not?

4.2 Similar issues arise with the provision of advice. What is appropriate advice? What is inappropriate advice? How well is an ATCO equipped to provide advice to a pilot flying an aircraft?

4.3 It is no coincidence that issues regarding the timely provision of appropriate information and advice to pilots forms the basis of so many duty of care cases involving ATCOs. These are the types of questions that the duty of care principles proposed in para [3.4] are designed to help an ATCO answer.

Over servicing

5.1 The concept of over servicing is a familiar one for many ATCOs. It often comes about because the ATCO is aware of the obligation to provide ‘advice and information’ to pilots but may not be sure if it is ‘useful for the safe and efficient conduct of flight’. This uncertainty may result in the ATCO passing too much or unimportant information to the pilot. The old adage ‘when in doubt, spread it about’ sums it up quite nicely. Therefore, for the purposes of the paper, over servicing is defined as:

5.2 The often-used excuse for over servicing is that there’s no harm done by giving a pilot all the information that may (not will) affect the safety and efficiency of the flight. And in many instances, this can be true – particularly when it only involves information and does not involve a direct instruction. The rationale is that it is safer that the pilot has too much information than not enough. But this may not always be the case.

5.3 Sometimes providing too much information can have negative consequences. Collecting and passing all the information that may affect the safe conduct of flight takes time away from ATCOs and pilots to perform other, perhaps more important, tasks. Where information can be obtained by both the ATCO and the pilot, it can lead to duplicated and sometimes conflicting information. Consistently providing information over and above what’s required can also lead to incorrect assumptions regarding the required level of service.

5.4 Of course, what might be considered over servicing in one situation might not be in another. It’s not hard to imagine circumstances where providing more information might be not only desirable but necessary for the safe conduct of flight. For example, the level of information or the service provided may vary with the experience of the pilot.

5.5 Over servicing can occur in a number of scenarios. The paper will examine over servicing with respect to the passing of traffic information in class G airspace.

Over servicing and traffic information in class G airspace

6.1 The concept of over servicing is often discussed in the context of when and to whom does the ATCO have to pass traffic information to in class G airspace. Are they required to pass information on VFR traffic to IFR traffic? If yes, when should the information be passed? What about VFR to VFR traffic? What about IFR to IFR traffic?

6.2 This paper will focus on the requirements to pass traffic in class G airspace. Similar issues also arise in class D, E and F airspace. However, these classes of airspace have slightly different requirements to those of class G airspace and, in the interests of brevity, these will not be considered for this paper.

6.3 ICAO Requirements for traffic information in class G airspace

6.4 In order to define what over servicing is in the context of passing traffic in class G airspace, we need to start with a baseline. In this case, the baseline will be the requirements of Annex 11 and Procedures for Air Navigation Services – Air Traffic Management (PANS-ATM)( International Civil Aviation Organisation (ICAO), Procedures for Air Navigation Services – Air Traffic Management (ICAO, 16th ed, 2016)). Of course, the service offered to aircraft in class G airspace may differ from that in PANS-ATM if desired by the State. On one end of the spectrum are the States that strictly comply with the ICAO rule set but other States amend it to address their own requirements. In Australia for instance, the rules for passing traffic in class G airspace are not in accordance with ICAO rules. Readers should be mindful of these when considering some of the examples in this paper.

6.5 As per the ICAO ATS Airspace Classes (International Civil Aviation Organisation (ICAO), Convention on Civil Aviation (“Chicago Convention”), 7 December 1944, (1994) 15 U.N.T.S. 295, Annex 11, Appendix 4), in class G airspace, ATC provide a flight information service to IFR and VFR aircraft. A flight information service includes information on ‘collision hazards’ to IFR aircraft. However, only information on ‘known aircraft’ which might constitute a collision hazard will be passed and it will sometimes be incomplete. Furthermore, air traffic services cannot assume responsibility for its issuance at all times nor for its accuracy. Of note also is that the flight information service provided to VFR flights does not include information concerning collision hazards. In other words, information on collision hazards should only be given to IFR aircraft receiving a flight information service.

6.6 PANS-ATM in Part 8.8 – EMERGENCIES, HAZARDS AND EQUIPMENT FAILURES contains a section on collision hazard information. It requires that when an identified IFR flight operating outside controlled airspace is observed to be on a conflicting path with another aircraft, the pilot should be advised ‘as to the need for collision avoidance action to be initiated’. Note this is not limited to ‘known aircraft’ as per Annex 11, and therefore appears to be a stricter requirement for passing information that may be a confliction hazard.

6.7 Summarising, for the purposes of whether or not to pass traffic, the questions for the ATCO becomes what is a ‘known aircraft’ and what ‘might constitute a collision hazard’ to the IFR aircraft receiving the flight information service? These elements will be considered separately.

6.8 What is a ‘known aircraft’?

6.9 ‘Known aircraft’ is not defined in either Annex 11 or PANS-ATM. However, it may be possible to draw some conclusions from the context in which the term used. In Annex 11, there are no additional references to ‘known aircraft’ other those previously discussed (para [6.4]). In PANS-ATM, there are several references to known and unknown aircraft in the context of providing collision hazard information.

6.10 PANS-ATM requires that ‘when an identified controlled flight is observed to be on a conflicting path with an unknown aircraft deemed to constitute a collision hazard, the pilot of the controlled flight shall, whenever practicable, be informed of the unknown aircraft’.

6.11 Similarly, when an identified IFR flight operating outside controlled airspace is observed to be on a conflicting path with another aircraft, traffic should be passed.

6.12 These references are consistent with a definition of unknown aircraft being aircraft for which the ATCO is unable to determine the identity of with any certainty.

6.13 The United Kingdom defines an unknown aircraft as ‘a position symbol which cannot be associated with an aircraft known to the controller’. (Civil Aviation Authority (UK), CAP 493 – Manual of Air Traffic Services (UK) (7th ed, 28 Dec 2017) at 15.1)

6.14 In New Zealand, an aircraft target is considered to by unknown ‘when the radar controller is unable to relate it to a particular flight known to be operating in the airspace concerned’. (Airways Corporation of New Zealand, Manual of Air Traffic Services (NZ) (14 Sep 2017) at 28.2)

6.15 In Canada, a known aircraft is an ‘aircraft of whose movements ATS has been informed’. (Nav Canada, Manual of Air Traffic Services (Ottawa, 1.2 ed, 2017) at p.60)

6.16 Summarising these definitions and the contexts with which they’re used, a ‘known aircraft’ 6.16. appears to be one that is in class G airspace, in an area for which the ATCO is responsible for providing a flight information service and whose identity the ATCO is aware of. Conversely, an ‘unknown aircraft’ is an aircraft in class G airspace, in an area for which the ATCO is responsible for providing a flight information service and whose identity they are not aware of.

6.17 What constitutes a ‘collision hazard’?

6.18 ‘Collision hazard’ is not defined in Annex 11. Nor is the context in which the term is used very useful. In a now expired Advisory Circular, the Federal Aviation Authority (USA) defined a hazard as ‘a condition that might cause (is a prerequisite to) an accident or incident’.(Federal Aviation Authority (USA), AC 120-92A (expired Jan 8 2015) at p. 6) In the absence of any definition, it may be reasonable to define ‘collision hazard’ as the plain meaning of the words – where there is a risk of a collision between aircraft or between an aircraft and/or terrain, a collision hazard exists.

6.19 As to how to determine if a collision hazard exists, PANS-ATM provides a little guidance. When an identified IFR flight operating outside controlled airspace is observed to be on a conflicting path with another aircraft, the pilot should be informed so they can effect collision avoidance action as required. This appears to offer two criteria: the aircraft are on a conflicting path and, interestingly, there should be a need for a pilot to take avoiding action.

6.20 This accords with an observation in Bennett v National Transportation Safety Board (66 F.3d 1130 (10th Cir. 1995) at 1132) where the court found that the need by an aircraft to take ‘evasive manoeuvres to avoid another aircraft is evidence of a potential collision hazard’.

6.21 Rather than leave it for the ATCO to decide if an aircraft will constitute a collision hazard, some States make their own rules and standards for passing traffic outside controlled airspace. For instance, the Netherlands has developed parameters as to when traffic should be passed. In that case it is when aircraft will come horizontally less than 1000FT AND less than 5NM horizontally apart from each other – essentially the surveillance separation standard in controlled airspace. Whilst this gives certainty to the ATCO when deciding whether or not to pass traffic to an IFR aircraft, arguably it is in excess of the standard required by the ICAO rule set.

6.22 Summarising, for the purposes of passing information to IFR aircraft receiving a flight information service in class G airspace, an aircraft may constitute a collision hazard if the ATCO observes it on a conflicting path such that evasive action may need to be taken to avoid a collision. Alternatively, if the aircraft are not on a conflicting path and evasive action will not need to be taken, then traffic information should not be passed as part of a flight information service to IFR aircraft in class G airspace.

Consequences of over servicing in class G airspace

7.1 Using the definitions above, IFR aircraft in class G airspace known to ATC must be informed of both known and unknown aircraft on a conflicting path such so that the pilot can take any evasive action that needs to be taken.

7.2 Of course, without knowing the intention of the pilot, it can be difficult to assess what constitutes a collision hazard and therefore when, and to whom, should information be passed. Are aircraft operating in proximity to each other in class G airspace always a collision hazard?

7.3 Often, rather than assess this, it’s easier to pass traffic information on any observed traffic within the vicinity of the IFR aircraft receiving the flight information service whether or not they are known or unknown or if they constitute a collision hazard or not. Where this information is not useful for the safe and efficient conduct of flight, it is over servicing as per the definition proposed in 5.1. Of course, the question can be asked that if there are no negative consequences to over servicing why not pass traffic?

7.4 However, there may be negative consequences to over servicing. Firstly, providing too much irrelevant information to pilots may be problematic. The pilot will still have to assess the traffic and decide what action, if any, may need to be taken. Pilots do not have the benefit of surveillance to quickly assess traffic. Because of the clear ‘information superiority’ of the ATCO, pilots may place greater reliance on the traffic information than the actual circumstances may dictate.

7.5 Although unlikely, it’s not inconceivable that a pilot may assume that because the ATCO has the better traffic ‘picture’, and that because the traffic has been passed, by definition it constitutes a collision hazard. The pilot may then prioritise the assessment of the traffic, and whether or not avoiding action may need be taken, over other tasks. This could result in the incorrect prioritising of tasks or ‘information overload’.

7.6 Continuous and systematic over servicing can also lead to pilots developing false expectations as to what service is provided. Where pilots are routinely issued with unknown traffic that does not constitute a collision risk, it’s not unreasonable for them to develop an expectation that ATC will always pass traffic that potentially affects them. This may lead to pilots being less vigilant for VFR traffic, a responsibility that is clearly the pilots, because they will be under the false assumption that ATC has passed them any traffic in the vicinity.

7.7 Not only could the pilot assume they are in receipt of all traffic in the area, if they are not passed traffic by the ATCO, they may assume there is no traffic in their vicinity. The irony of this situation is that where the ATCO provides a flight information service to an IFR aircraft in class G airspace in accordance with ICAO Annex 11, and only passes known traffic that may constitute a collision risk, it may introduce more risk. This is because as a result of previous over servicing, and having been not ‘over serviced’ in this instance, the pilot may incorrectly assume there is no traffic and not be as vigilant for other aircraft.

7.8 Continuous and systematic over servicing may also have consequences for ATCOs. As in para 3.2, an ATCO owes a duty of care to pilots and their passengers. The standard of care is that of the reasonably competent ATCO. This standard is mostly measured against the standards and procedures prescribed by regulations and operations manuals – the ATC rule set. However, in some jurisdictions, a court will look to the actual practices of ATCOs to define the standard even though it may not be strictly in accordance with the ruleset. This may be the case where pilots have come to rely on over servicing.

7.9 Effect on the ‘standard of care’ by over servicing

7.10 The standard of care required by ATCOs is that of a reasonably competent ATCO.24 They need not possess the highest expert skill, just the ordinary skill of a competent ATCO.(Bolam v Friern Hospital Management Committee (1957) 2 All E.R. 142 at 144 in C Shawcross and K Beaumont, Air Law (Butterworths, 4th ed, 1977), p 78) Of course, what constitutes a ‘competent ATCO’ becomes an important question.

7.11 Although not definitive, in some jurisdictions, the courts may look to the common practices of ATCOs to determine what is competent – that is, what is the standard of care.(Rogers v Whittaker (1992) 67 ALJR 47) Where there are a substantial number of ATCOs that consistently provide advice and information over and above that required by the rule set, this practice may set the standard of care that all ATCOs must meet. In other words, over servicing by a number of ATCOs in a group may result in the over servicing becoming the standard of care and not the standard actually required by the rule set.

7.12 On a similar note, in the United States there is a doctrine known as a the ‘Good Samaritan Doctrine’ that a duty arises out of reliance. In an ATC context, if an ATCO undertakes to exercise a practice which gives rise to reliance, they have a duty to continue that practice with due care.(Bigwood, R, ‘The Civil Liabilities of Air Traffic Control Personnel in New Zealand’ (1987) 5 Auckland U. L. Rev. at 431) Or put another way, if the ATCO undertakes an act that engenders reliance, it must continue to perform that act with due care or be held to be negligent. (Early et al, ‘The Expanding Liability of Air Traffic Controllers’ (1973) 39 J. Air L. & Com. at 615)

7.13 In terms of providing a flight information service in class G airspace, it may be that an ATCO who passes traffic in accordance with Annex 11, (i.e. only known traffic that may constitute a collision hazard) may not be meeting the required standard of care because the standard of care has been changed due to over servicing, and it is now above what is actually prescribed by the rule set.

Application of duty of care principles

8.1 Whilst the definition of ‘known aircraft’ is relatively easy to apply, the lack of prescriptive definition of what constitutes a collision hazard means that it can be left to the ATCO to use their judgement. It is situations like these that duty of care principles proposed in section [3.4] may be useful. These principles are that the ATCO has a duty to:

1. make reasonable efforts to obtain and maintain information to ensure the safety of aircraft in their area of responsibility;

2. reasonably act on information so as to ensure the safety of aircraft in their area of responsibility; and

3. pass information to the pilot, in a timely manner, that it’s reasonable to assume the pilot will rely on to ensure the safety of their aircraft?

Obtain and maintain information on traffic

8.2 What information is the ATCO required to obtain and maintain to ensure the safety of the aircraft? Assuming the ATCO is operating in a surveillance environment, it’s reasonable to expect that the ATCO be vigilant with regard to known and observed (unknown) traffic in their area of responsibility. This is not to say that workload will not play a part in how vigilant a controller must be. It’s reasonable that if an ATCO’s area of responsibility covers both controlled and uncontrolled airspace, should the controlled airspace portion require extra attention, there may be less awareness of observed but unknown traffic in the uncontrolled portion of their airspace.

8.3 However, it is reasonable that, for example, an ATCO providing an IFR aircraft operating in an area with significant unknown traffic with a flight information service (which includes information on collision risks) will obtain and maintain information on other aircraft that may constitute a collision risk. This may also include maintaining a listening watch for any information that may be broadcast by unknown aircraft that may be helpful in assessing whether or not a collision risk may exist for the aircraft being provided the flight information service.

8.4 Reasonably act on information

8.5 The second ‘duty of care’ principle is that the ATCO should act on information that it would be reasonable to conclude will ensure the safety of aircraft in their area of responsibility. Acting on information could mean passing it to a pilot in a timely manner or it could mean the ATCO issuing an amended clearance or initiating avoiding actions.

8.6 In the context of this scenario, because the aircraft is outside controlled airspace, if the ATCO concludes the information will be relied upon by the pilot, the ATCO will pass it to the pilot to act upon. In this case, satisfying the second principle will result in applying the third principle.

8.7 Pass information it’s reasonable to assume the pilot will rely on

8.8 The concept of reliance has been recognised as a significant factor when considering whether an ATCO’s has achieved the required standard of care. Broadly, the ATCO should pass to the pilot any information that it would be reasonable to assume the pilot would rely on to ensure the safety of the aircraft. The reverse of this proposition is that the ATCO does not have a requirement to pass the pilot information that they would not rely on.

8.9 A pilot might not rely on information for several reasons. The information could be irrelevant. The information could be relevant but not useful to ensure the safety of the aircraft. Or the pilot may have access to the same or better information from other sources. All of these could be factors an ATCO may consider when deciding what information to pass to a pilot.

8.10 For instance, for the purposes of deciding what constitutes a collision hazard when providing a flight information service to an IFR aircraft in class G airspace, if the ATCO reasonably concludes that two aircraft are not on a conflicting path and no collision avoidance action will need to be taken, it would be reasonable not to pass traffic. If the ATCO decided to pass traffic to the IFR aircraft on unknown VFR traffic that was in the general area but not on a collision path, then arguably this would be over servicing.

8.11 If it’s reasonable to assume that any unknown VFR traffic in the vicinity were operating in accordance with their requirement to remain in visual meteorological conditions (VMC) and use alerted see and avoid, to avoid collisions, then, without any other information, it may also be reasonable for the ATCO to conclude there is no collision hazard that warrants the passing of information. Furthermore, depending on what airspace rules apply, the requirement for pilot reports in the vicinity of aerodromes for instance, it may also be reasonable for the ATCO to assume pilots will correctly apply these rules. This could lead an ATCO to reasonably conclude that there is little reason to be concerned with collision hazards, even when aircraft are operating in reasonably close proximity to each other.

8.12 This is why the concept of reliance can be important when deciding what information a pilot may require to ensure the safety of the aircraft. The greater the reliance by the pilot on the ATCO, the greater the requirement on the ATCO to ensure they have the information they require.

Conclusions

9.1 The concept of over servicing is a relatively easy concept to grasp but difficult to define. Many ATCOs have developed their own ‘principles’ of service provision that they apply when the ‘black and white’ rule set doesn’t. However, what needs to be considered is that individual principles don’t operate in isolation. Different principles affect the level of service being offered and these affect pilot expectations. These expectations may continue to operate long after the ATCO applying them has ‘unplugged’ and may have negative consequences.

9.2 It’s important that ATCOs operate in a standard manner as much as possible. Ideally this is achieved by acting in accordance with national (and international) rules. Where these rules are ambiguous, duty of care principles may offer a methodology to standardise ATCO practices where they currently are not standardised. This paper focuses on one area where this may be the case – the provision of traffic information to IFR aircraft in class G airspace.

Recommendation

10.1 It is recommended that the paper be accepted as information.

10.2. It will be recommended to the Executive Board to give consideration for the information contained within be reproduced in a ‘leaflet’ format to be circulated to Member Associations for information.

References

Books and Articles

Bigwood, R, ‘The Civil Liabilities of Air Traffic Control Personnel in New Zealand’ (1987) 5 Auckland U. L. Rev.

Early et al, ‘The Expanding Liability of Air Traffic Controllers’ (1973) 39 J. Air L. & Com.

R Hansman, H Davison, ‘Effect of Shared Information on Pilot/Controller and Controller/Controller Interactions’ in L Bianco et al (ed), New Concepts and Methods in Air Traffic Management (Springer, 2001).

U Magnus, ‘Tort law in general’ in Jan M Smits (ed), Elgar Enyclopedia of Comparative Law (Edward Elgar Publishing, 2nd ed, 2012).

Technical Documents

Airways Corporation of New Zealand, Manual of Air Traffic Services (NZ) (14 Sep 2017) Civil Aviation Authority (UK), CAP 493 – Manual of Air Traffic Services (UK) (7th ed, 28 Dec 2017).

Federal Aviation Authority (USA), AC 120-92A (expired Jan 8 2015).

International Civil Aviation Organisation (ICAO), Convention on Civil Aviation (“Chicago Convention”), 7 December 1944, (1994) 15 U.N.T.S. 295, Annex 11.

International Civil Aviation Organisation (ICAO), Procedures for Air Navigation Services – Air Traffic Management (ICAO, 16th ed, 2016).

Nav Canada, Manual of Air Traffic Services (Ottawa, 1.2 ed, 2017).

PLC, ‘ATCO Duty of Care’ paper presented to the International Federation of Air Traffic Control Associations (IFATCA): 56th Annual Conference, Toronto, 2017.

Cases

Bennett v National Transportation Safety Board 66 F.3d 1130 (10th Cir. 1995).

Bolam v Friern Hospital Management Committee (1957) 2 All E.R. 142 at 144 in C Shawcross and K Beaumont, Air Law (Butterworths, 4th ed, 1977).

Rogers v Whittaker (1992) 67 ALJR 47.