Making Decisions is Hard: How Long Must a RESA Be?

A couple of months ago, the New Zealand Court of Appeal handed down a judgement against the NZ Civil Aviation Authority's (CAA)  assessment of Runway End Safety Area (RESA) requirements stemming from their own rules. While not everyone is in to reading court decisions and pulling apart regulations, I obviously am. As such, I thought I would save you the trouble and write about it here.

The Context

Wellington Airport wants to extend its runway and it's going to cost a lot of money. In planning for and designing this extension, the airport operator requested a clarification from the NZ CAA on their RESA length requirements. 

In support, the operator provided a cost-benefit analysis report they had commissioned and in opposition, the NZ Air Line Pilots Association (NZALPA) critiqued this report. The NZ CAA Director communicated that he did not think it practicable for the operator to provide a RESA greater than 90 metres. NZALP disagreed and launched legal action against the airport operator and the NZ CAA.

The Decision

The Court set aside the NZ CAA Director's decision and directed him to reconsider inline with the details contained in the judgement. For me, those details revolve around two key questions.

  • What is meant by practicable?
  • What is the acceptable minimum?

But First, the Rules

The NZ implementation of the International Civil Aviation Organisation (ICAO) RESA Standards And Recommended Practices (SARPs) looks like this:

(a) A RESA must extend—
(1) to a distance of at least 90 metres from the end of the runway strip, and
(2) if practicable
(i) to a distance of at least 240 metres from the end of the runway strip; or
(ii) to the greatest distance that is practicable between the 90 metres required in paragraph(a)(1) and the 240 metres required in paragraph (a)(2)(i).

I've emphasised the key words in the rule above.


The Court has seemingly clarified what can and can't be considered as part of the NZ CAA Directors decision where the word practicable is concerned. It this case the biggest lesson comes from what is to be left out - cost.

Instead, the Court stated that the meaning of practicable is well known and a matter of precedent. The Court defined it as "something that is feasible or able to be accomplished according to known means and resources". I guess one can infer that if it is possible to engineer a runway on reclaimed land (as is the case in Wellington) then it is practicable to engineer a RESA to the full length.

Absence of cost from the assessment did catch me off-guard. The judgement includes a couple of comments on why cost is not to be considered including changes made to the NZ CAA's primary legislation and the regulatory development process. Probably the easiest issue for me to understand was again pointing out something that was missing - this time it was the word reasonably.

To many in the safety word the phrase "reasonably practicable" is so standard than you almost can't be blamed for reading one into the other. But, sorry, the Court says "no". Had the rule included the word, then the Court recognises that it could be "seen as affording greater latitude to adopt an (sic) cost-benefit analysis". However, this rule does not include the adverb and therefore must be interpreted in the stricter sense.

But where does that leave us? Airport engineers can do some pretty amazing things. Reclaiming land is almost standard for low-level coastal airports (see Hong-Kong or Brisbane) and even elevated structures are becoming common (see Fort Lauderdale-Hollywood or the amazing Madeira). So what limitations exist?

Outside of pure engineering limitation, could being limited by space in a land-locked sense be a legitimate source of impracticability. I know there are a lot of people looking at these questions now and it will be interesting to see what they come up with. It looks like the parties are heading back to court so this story isn't over yet.

The Acceptable Minimum

This aspect of the judgement is probably the more boring part (for normal people) but it also contains some important lessons for those of us that write anything like rules or procedures that others must follow. This issues really drives home that how you write something is almost as important as what you write.

If I asked you to answer the question "what is the minimum distance a RESA should be?" would you answer: 

  1. "pfft, easy, 90 metres"; or
  2. "well actually Dan, it would be the minimum practicable distance between 90 and 240 metres"?

The Court goes to great lengths to not only say that the answer is b. but to make sure that the starting point is determining if 240 metres is impracticable and then winding it back until until it becomes practicable or you reach 90 metres.

It is easy to sit here and suggest alternate ways that this rule could have been constructed but the challenge will be to avoid this issue in the future. And this is not just a regulator lesson. If you are writing airside driving rules, it applies. If you are writing a airport emergency plan, it applies. If even applies to writing out a simple procedure. We need to think about who is reading the words and how they are going to apply them.

I once had a CEO demand we write processes and procedures so that his mother could pick them up and follow them. I don't think this is a bad approach to have but you'll need to check whether she is available first.

I mentioned the return to court in the section above because I think that the issue surrounding the interpretation of practical is more contentious and this issue seems more procedural. I guess we shall see. Even if the NZ CAA Director's interpretation of this rule construction is found valid and reasonable, it still seems like a lot of time and money has been spent on something that could have been avoided.


Obviously, this decision only applies in New Zealand. But the issues may highlight potential issues in other countries. I did a quick review to see how some other countries define their RESA requirements. 

If you're interested please feel free to read on and either way, please take the time to provide some feedback in the comments area below.


The Mothership - ICAO

Since Annex 14 is the source of from which the NZ rules and most other rules come, it is important to check in with them first. It was directly referenced in the Court's decision as well. On the subject of RESA lengths, the Annex 14 says*:

3.5.2 A runway end safety area shall extend from the end of a runway strip to a distance of at least 90 m. 
3.5.3 Recommendation — A runway end safety area should, as far as practicable, extend from the end of a runway strip to a distance of at least:
— 240 m where the code number is 3 or 4; and
— 120 m where the code number is 1 or 2

So ICAO makes a distinction between the standard of 90 metres is expects states to comply with (subject to article 38) and the 240 metre recommendation that states should endeavour to meet. The word practicable appears without its friend, reasonably but the inclusion of as far as suggests the variable length concept of achieving a maximum practicability comes from ICAO. The whole construction clearly requires each state to turn these two expectations into a rule for their jurisdiction.

* I think I have an old version of Annex 14 and I don't have access to get the latest.

The Motherland - Australia

In Australia, the rule for the length of a RESA is found in the Manual of Standards Part 139 and it says: The minimum length of the RESA must be 90 m where the associated runway is suitable for aircraft with a code number 3 or 4 and is used by air transport jet aeroplanes. In other cases, the minimum RESA length must be 60 m.
Note: Additional length of RESA should be provided especially at international aerodromes, in accordance with the following ICAO recommendations:
1. if the runway’s code number is 3 or 4 — 240 m; or
2. if the runway’s code number is 1 or 2 — 120 m.

Here, CASA is using a similar distinction to ICAO in providing a must/shall standard and a should recommendation. Where CASA uses terms such as practicable, it reserves the right to determine what this means but in the case of recommendations, the MOS is silent on who makes the call.


EASA's aerodrome design rules set out the RESA length requirements as follows:

CS ADR-DSN.C.215 Dimensions of runway end safety areas
(a) Length of runway end safety area
(1) A runway end safety area should extend from the end of a runway strip to a distance of at least 90 m and, as far as practicable, extend to a distance of:
(i) 240 m where the code number is 3 or 4 and
(ii) 120 m where the code number is 1 or 2 and the runway is an instrument one; and
(2) A runway end safety area should extend from the end of a runway strip, as far as practicable, to a distance of 30 m where the code number is 1 or 2 and the runway is a non-instrument one. 
(b) Notwithstanding the provisions in (a) above, the length of the runway end safety area may be reduced where an arresting system is installed, based on the design specifications of the system. ...

This one is pretty close to ICAO with the recommendation folded into the standard to create one one rule similar to New Zealand's. I think the variable length requirement is clearer in the NZ CAA construction but the link to the larger 240 metre requirement is clearer from EASA. 


I picked a relatively new aviation state to look at their construction and from the Qatar Civil Aviation Authority we get:

3.5.4 A runway end safety area shall extend from the end of a runway strip to a distance of at least:
a) 240 m where the code number is 3 or 4; or a reduced length when an arresting system is installed;
b) 120 m where the code number is 1 or 2 and the runway is an instrument one; or reduced length when an arresting system is installed; and
c) 30 m where the code number is 1 or 2 and the runway is a non-instrument one.

No 90 metre option here but reduction is possible if an arresting system is installed. This construction is quite easy to understand and probably suits the environment with rather new airports.


Transport Canada's application of RESA standards is interesting to read. Simple and similar to the outcome above in that it specifies a single length requirement reducible only through an engineered arresting system. It says: The runway end safety area:
(a) has a minimum width twice of the associated runway;
(b) extends away from the runway;
(c) is centred on the extended runway centreline; and
(d) subject to section, has a minimum length of 150 m to the end of the RESA.
Note: The 150 m length is inclusive of the runway safety area beyond the runway end. Where a recognized EMAS is installed within the RESA and complies with section, the overall RESA length may be reduced.

Only 90 metres for Canada (150 m - 60 m runway strip). I had heard that Canada had not yet implemented the 240 metre RESA requirement but it still caught me by surprise to not even see a recommendation.

I probably could go on but I need to go to bed! Please leave a comment below if I have missed your country's approach to RESA requirements.

Header image from Karelj.