View Full Version : The limitations of "See and Avoid"

4th Dec 2003, 19:04
G'day All,

this is my first PPRUNE post - till now I've been happy enough to just "listen and learn" - after all, being a low-time PPL (VFR and PIFR) there's probably not a lot I could say that you don't already know.

However I would like to make a point about the reliance on "see-and-avoid". While it's fine in principal, in practice it leaves a lot to be desired.

I know this topic has been covered before but I think it's VERY IMPORTANT that the powers-that-be understand that relying on see-and-avoid (oh, and a transponder which is hopefully working) is flawed.

I fly only a few times a month (out of Bankstown) and I for one can think of many situations where I'll now feel very uncomfortable with the concept of being in airspace where there *may* be other aircraft - however due to the "no chatter" edict I won't know they're there (and vice-versa).

I did a search on "limitations of see and avoid" using Google (isn't the internet wonderful... sometimes ?)

Some interesting (saddening) things came back including...

The mid-air collision between PSA Flight 182 (B727) and a Cessna 172 in 1978 over San Diego.
(I'm not going to go into it - there's a lot of gory detail about it on the internet). One area that is worth highlighting however is that in the NTSB report (http://www.cactuswings.com/psa/museum/NTSBAAR7905.pdf) it mentions the following:

Cockpit Visibility Study

The cockpit visibility study was based on a series of photographs taken with a binocular camera mounted within the cockpit of a Boeing 727-200 series aircraft at the design eye reference points for the pilot and copilot seats and at an arbitrary eye position for the observer seat. Similar photographs were taken from inside the cockpit of a Cessna 172 with the camera mounted at the pilot's design eye reference point. Another set of photographs was produced for the Boeing 727 with the camera mounted 5 ins. forward of the pilots' normal design eye reference points and represents a pilot leaning forward 5 ins. to search for an airborne target. This position was called the alert position.
Since the exact position of the flight engineer's seat during this part of flight could not be determined, binocular photographs were not made for his position.

The photographs show a panoramic view of the window configuration as seen by the crewmember as he rotates his head from one extreme side to the other. Visibility from the right cockpit seat was simulated by reversing the negative of the photograph taken fron the left cockpit seat. A grid of horizontal and vertical lines in 5" increments was superimposed over the photographs. Each photograph contains 17 points which represent the calculated location of the target aircraft on the viewing aircraft's windshield from 170 sec to 10 sec before the collision.

The points --which are numbered from 1 to 17--were plotted at 10-sec intervals. The plotted target points take into account the heading, and bank angle of the viewing aircraft.

The photographs taken from the captain's and first officer's seats showed that the Cessna would have been almost centered on their windshields from 170 sec to 90 sec before the collision, and thereafter it was positioned on the lower portion of the windshield just above the windshield wipers. Movement to the alert position elevated the position of the Cessna targets during the last 80 sec slightly. The view from the observer's seat showed that the Cessna target, for the most part, would have been hidden by the captain's head and shoulders and aircraft structure.

The photographs taken from the Cessna showed that at 90 sec before the collision Flight 182 would have been positioned on the upper portion of the left door window for about 10 sec. The remainder of the time it was hidden behind the cockpit's ceiling structure.

The Boeing 727-200 series is equipped with a design eye reference point locator on the post between the two windshields to provide guidance to both pilots in adjusting their seats so that their eyes are near the design eye reference point. The device consists of three balls in a triangular arrangement, two of which will be aligned when each pilot's eyes are near the design eye reference point. Several members on the Safety Board's Visibility Study Croup sat in the left and right pilot seats and adjusted the seat using the locator device until, in their judgment, their eyes were at the design eye reference point.
Each subject reported that, with their seat so adjusted, the glareshield did not mask or interfere with their view of the instrument panel displays.

Federal and company regulations do not require pilots to adjust their seats so as to position their eyes at the design eye reference point. The chief pilot of PSA testified that he and other company pilots are not able to either move the aircraft's rudder pedals and elevator column to their stops, or see the entire instrument panel when the pilot's seat is positioned to place their eyes at the design eye reference point. In order for him to obtain full use of the controls and full visibility of the instruments, it was necessary to move his seat slightly aft. He also testified that the company recommends that the pilot position his seat to place his eyes at the design eye reference point, and then move it as little as possible to scan all his instruments and have full displacement of the aircraft controls. According to him the seat movement to achieve this was "probably no more than 1 inch aft." However, other company pilots stated that the seat had to be moved both aft and down.

...I'll let you draw your own conclusions...

Another tragedy occurred in 1960 over Paris - this time between a Caravelle and a Stampe.

(see: http://aviation-safety.net/database/1960/600519-0.htm)

It looks like the words have been translated from the French... but the final paragraph sums it up (and this was in 1960)...

CONCLUSIONS: "Literal application of the Rules of the Air (RAC 1 -3-02) elicits the statement that it was incumbent on both pilots-in-command to avoid collisions that the pilot of the Stampe, being on the the right, had the right-of-way (RAC 1-3-02 of 1 July 1959). However, the results of the inquiry, lead to the contention that such regulations are no longer adapted to the speeds and procedures practiced by jet aircraft, the pilots of which cannot be sure of avoiding any risk of collision by visual means alone."

Source: ICAO Aircraft Accident Digest, Circular 64-AN/58 (174-179)

Also: http://www.iflyamerica.com/midairs.htm
The 329 midair collisions indicate that see-and-avoid has inherent limitations as a tactic or strategy for avoiding midair collisions. This is certainly true of midair collisions that involve high closing speeds, but it is also true of midairs that involve low closing speeds.

The human eye can detect and recognize an aircraft the size of a PA-31 or a comparable Cessna at a maximum of 1.5 miles. If the closing angle is head-on, or nearly so, even two small and relatively slow civil aircraft close at speeds in excess of 200 knots. This allows a maximum of 25 seconds for evasion under ideal conditions. However, the ideal is reduced by various factors, including the following.

First, substantial time is required to scan the horizon properly. The human eye requires small changes in the radial being scanned, plus time to focus on each new scan. To scan just 130 degrees of the horizon and focus on interim target areas, a pilot requires up to 20 seconds. A target aircraft may not be visible when the pilot scans and focuses on a radial and, by the time the pilot returns to that radial, closing time may be prohibitively short.
Ideal conditions also are reduced when a pilot's attention is focused inside the cockpit, where workload reduces the time a pilot spends scanning. Workload is highest during approach/landing and takeoff/climb-out, when most midairs occur.
See-and-avoid also is limited by the absence of visual contrast between a target aircraft in a clear or hazy sky, which substantially shortens the 1.5 miles. This is especially true when either pilot is flying toward the sun. In addition, high-wing aircraft restrict a pilot's ability to scan above his or her altitude, while low-wing aircraft restrict the ability to scan below the aircraft.
Any of the factors identified above can reduce the effectiveness of see-and-avoid. The combination of any two or more factors can reduce the practical time available for a safe, evasive maneuver to just a few seconds or less. This is true even where closing speeds are relatively slow due to closing from the rear, from above, or from quartering angles.

Does all this mean that see-and-avoid is useless or that it should be abandoned? Hardly! Though we know a lot about the characteristics of midair collisions, the fact is that we know relatively little about the role of see-and-avoid or other factors when collisions are narrowly avoided between two GA aircraft. No aviation safety agency in the world could, with a straight face, advise pilots to forget about visual scanning. In short, the point here is not that visual scanning and see-and-avoid lack any merit. Rather, see-and-avoid has real merit, but, as a primary strategy for further reductions in midairs, its limitations are equally real.

Other material includes:
"The Flight Safety Foundation" March 1994 report entitled "Limitations of See-and-avoid Concept cited in Fatal Midair Collision" which can be found at http://www.flightsafety.org/pubs/fsd_1994.html
(you'll need to create a Logon ID first).

A BASI report from 1991 (I haven't been able to find a reference for this).

And what does the NAS documentation say about this ? Well it does acknowledge that there are limitations to see-and-avoid (page 39 of the "Reference Manual") (http://www.dotars.gov.au/airspacereform/pilot_education/pilot_training_and_education.htm)

I won't quote it directly as they might try and do me for breaching copyright...

It says that as well as "see and avoid" we should :

fly at the correct hemispherical levels.... true, but unless you've got some sort of Star-Trek matter transference beam most of us have to climb / descend through other levels to reach the level we're going to...

use our lights.... fine, but bulbs do burn out, and pilots (believe it or not) have been known to forget to turn the lights on...

TCAS... nice if you have it... bummer if you don't... oh and if you DO have it, let's hope the other guy/gal has remembered to switch the transponder to ALT (and let's hope the transponsder hasn't gone U/S)...

That page in the Reference manual then goes on to say that during climb/descent please remember to not let the cockpit workload get too great that you don't spend your time looking out the window... hmmm...
possible (maybe) if you're multicrew but not very practical if you're flying solo.

Anyway, that's just my 2 cents worth... as I said I wouldn't normally clutter up the forum but this is too important - everyone needs to voice their concern about this dangerous situation.

5th Dec 2003, 04:05
BASI (1991) The Limitations of See and Avoid, Research Report, Bureau of Air Safety Investigation, Canberra. April 1991. ISBN 0 642 16089 9

Not available electronically as far as I know. E-mail me if you search and can't get a paper copy on account of the fact it has suddenly 'disappeared'.

Amongst its findings:
A traffic search in the absence of traffic information is less likely to be successful than a search where traffic information has been provided because knowing where to look greatly increases the chance of sighting the traffic (Edwards and Harris 1972).

Field trials conducted by John Andrews found that in the absence of a traffic alert, the probability of sighting a threat aircraft is generally low until a short time before impact. Traffic alerts were found to increase search effectiveness by a factor of eight. A traffic alert from ATS or from a radio listening watch is likely to be similarly effective (Andrews 1977, Andrews 1984, Andrews 1987).

One of the recommendations of that report was that 'pilots should recognise that they cannot rely entirely on vision to avoid collisions. Consequently, they should attempt to obtain all available traffic information, whether from Air Traffic Services or a listening watch, to enable them to conduct a directed traffic search.

However your thought that it's VERY IMPORTANT that the powers-that-be understand that relying on see-and-avoid (....) is flawed is probably going to be unfulfilled. One of the conclusions of the BASI 1999 INVESTIGATION REPORT B98/166 Systemic Investigation into the Class G Airspace Demonstration, pertained to the powers-that-be, and it was that The following organisational factors adversely influenced the ability of CASA to effectively
manage the Class G demonstration project:
• There was a lack of established processes within CASA for conducting safety case and
consultation activities for large change-management projects.
• CASA’s management profile and staffing prior to July 1998 reduced the ability of the
organisation to effectively monitor and control its activities.
• There was a lack of appropriate internal and external review mechanisms for ensuring the
objectivity of the project.
• The division of roles and responsibilities between CASA and Airservices Australia regarding the
design and regulation of airspace was not clearly defined.
• The division of roles and responsibilities between the CASA Chairman and the Director and
other management was not clearly defined.
• The influence of the CASA Chairman’s involvement in airspace reform and management style
contributed to the project management deficiencies associated with the demonstration. The only thing that seems to have changed is that Dick is no longer the Chairman, but he is still involved in airspace reform and the collective Smiths' management styles have very heavily contributed to the project management deficiencies associated with the present NAS introduction.

Let me finish with this marvellous quote from the 1999 BASI report which seems as relevant today as it was then The Chairman’s close involvement in project management became associated
with a number of undesirable consequences, including:
• the removal of previous internal review processes, including important review mechanisms
at higher levels than the decision-maker;
• a decrease in the ability of CASA managers, and the organisation as a whole, to coordinate
their decision-making processes;
• an increase in confusion among staff and external parties regarding who in CASA was
making decisions, and what decisions were valid; and
• uncertainty among CASA staff regarding their ability to query the Chairman’s decisions or
instructions due to his senior position.
It was subsequently reported by CASA staff that the Chairman’s management style was
characterised by micro-management, an unwillingness to consider other views, and rigid
adherence to a pre-determined path. The Chairman also appeared to show a low level of
interest in activities that could lead to delays in the implementation process.
Many of the problems associated with the planning and implementation of the demonstration
were related to inadequate safety analysis, consultation and education activities. Although
there were many reasons for the problems encountered, there is considerable evidence to
indicate that the influence of the Chairman’s active involvement and management style
contributed to those problems.

5th Dec 2003, 07:15

What a blood good post! Can I suggest you pick up all those points and include them in a letter to CASA and the ATSB?


Also a bloody good post! We need to find a way to publicise the BASI findings on the Chairman's role (maybe CloudSteet's website or a letter to the Minister?)

5th Dec 2003, 11:54
I'm not sure CASA is the people needing to know this information. It needs to get to Airservices Australia, but mostly to minister Anderson. Someone needs to deliver the info by hand to him and then make sure he reads it thouroughly!

5th Dec 2003, 14:26
There Are None So Blind As Those Who Will Not See

I like the posts here - shows some lateral thinking.

In regard to the blind bit, it's my experience that knowing where to look makes all the difference. That's not to say that Mr Average PPL will work out where to look, because many simply don't hear all radio calls fully, and many lack situational awareness to the extent that they are unable to work out where the traffic will / should appear. Much, much more instructor effort needed to bring pilots up to speed in these matters during BFR's.

RPT,RAAF,IFR and other professional pilots should try not to rattle off an inbound call at the speed of a Melbourne Cup call. I note that many pilots just don't understand the call, and this could in part be to not being able to 'hear' it. Professionals - it's up to you to set an example of clarity and pronunciation in your calls.

A recent example: Muffled call from RAAF PC9 inbound elicited a response from PPL, who responded I'm 13 miles to the SE. So far so good - but then PC9 wants to know the pilots radial and distance PPL just doesn't respond to this because he doesn't know what the bloody RAAF are doing if they can't understand his initial call. Next thing - RAAF responds forget it Not a very understanding attempt by the professional in this case.

I am hearing much angst in regards to frequencies. Many are simply staying on 126.70 everywhere. OK - until you get to somewhere with a different CTAF frequency! The real problem between Centre and MBZ/CTAF changeover is that there is such a difference between aircraft speeds, and traffic can conflict simply because so much time has elapsed since initial calls. In a 15 kt headwind, a C172 could take 11-12 mins to do 15nm, whereas a 240 kt turbine will do it in under 4 mins. The turbine wouldn't have a clue about the 172, despite the best intentions of both pilots.

The other issue is where there is fast traffic both ways - 160 kts + 240 kts results in a crossing time of just over 2 mins since a 15nm call. Too close!

I think we have it all wrong here. Why not have people report in @ say, 8 mins from the airport - forget the distance. So the turbine might well be pre TOD, but, what's wrong with that? They usually monitor the CTAF/MBZ frequency well in advance anyway.

I'm not hearing much about emergency situations. It doesn't seem to be a big deal for most - you can use Centre if you know it, but 126.70 would be OK as there are plenty of aircraft on it. There's also 121.50, although many pilots are afraid to use it in case of mistakes.

As usual with changes, it will take time for things to adjust. I think that the NAS has greatly,grossly,immensely,ignorantly overestimated the abilities of Mr Average PPL, and has not made provision for instructors/flight schools to teach the system. In fact - we've been sidelined by NAS trying to do it by direct mail - most of which is still sitting in Mr Average PPL's navbag, because it looked too bloody hard.

I say overestimated with some knowledge of what Mr Average PPL is capable of - I do a lot of BFR's. Let me explain:

situational awareness - not a clue when it comes to traffic, but most could navigate to Widgiemooltha on a dark night -without a map!

TXP/C serviceable and operating - why isn't the light flashing? (we're 200nm from radar!!)

COM is on correct frequency - sure is, but the volumes down, the audio panel switch is rusted in no-mans land, and that bloody cabin speaker's been useless since I bought this thing in 1965 - bewdy!

Avoids IFR approaches and dense traffic areas - jeez, where's it say anything about that on my Country Road Directory? Would willingly deviate via Meekatharra to avoid talking to those guys!

Uses Landing Lights - you're joking, they're on the 'cruiser we use for shooting! Anyway, I'm having alternator trouble.

Understands VMC/VFR - yeah, I always keep outa cloud, but it means lots of bugs on the wings, and sometimes people complain about my being a bit, er... low. (stop worrying RPT, this guy will only ever worry you on a LJR)

Should we let 'em loose in E? Hell no! Refer to the 'blind' bit.

Most of them don't aspire to anyway, but they are going to mix it with everyone else in MBZ/CTAF.

And this is where I beleive the risk is greatest, because if people are unsure of their position, don't speak because they're unsure or want to avoid landing charges, don't understand what's being said by others, and don't really understand their radio gear - where are we?

This industry has a lot of awareness work left to do, and frankly, CASA would be better giving their budget to we instructors to fix things, after making a few changes to the structure of it-all over again!