Hi Guys,

I just have a few questions regarding the performance exam.
- There seems to be no clear rule that CASA wants us to follow in exams as to whether you include the slope or not in T/O & LDG charts. I understand that legally we don't need to account for it if it's less than (or including) 1%, however, I've seen many people out there that say to include it, and others, to not. Perhaps Bob, you might be able to shed some light as to what CASA wants specifically in these exams.
- In an Echo question, if it doesn't specifically say that we cannot put cargo on seats, can we assume we can (up to 77kg with a seat still in place)?
- Is CASA moving to a more 'boxed/numbered' answer approach to chart questions, or is it still a mix between multiple choice and the former.

Cheers for the help!
B

Some things to consider -

(a) the slope question comes up periodically for discussion so you might like to spend some time in the Search function to review previous threads, eg,
www.bobtait.com.au/forum/performance/558...arts-cao-20-7-4#9702

(b) As best I can recall, the 1% stuff has been around for a long time - I probably have some archived ANOs dating back to the early/mid-60s (when I first started playing around with aeroplanes) somewhere in the filing cabinets and, I suspect, it was there, then. I have no idea whence it arose but suspect that it would be back in Icko's early days in Airworthiness (a most wonderful and charming gentleman of the old school who died several years ago, now - www.smh.com.au/national/icko-tenenbaum-a...-20131208-2yz73.html). Mind you, those of us who worked with him had the occasional robust discussion on engineering matters but, always, in a dignified and gentlemanly manner.

My best guess is that it will have been tied up with strip length certification for those early aircraft which didn't have any P-chart data, but that's only an educated guess. I suggest that it originated in the Airworthiness ANOs (101.22 for lighties or, quite likely in the earlier ANOs which had titles including numerous dots and numbers .. as I recall, the last of those shuffled off in the late 60s) and then was copied across into the operational series (20.7)

(c) So what might it mean ? Yes, the rulebook provides a concession for low slope, reflecting the relative significance of the correction. Refer to CAO 20.7.4.4.1(a) and 5.1(a). However, if the charts you have available have a slope correction, generally it will cover a range from down through level to up. There is absolutely NO sensible reason not to use the correction on the chart for shallow slopes .. so, I suggest, use it.

If the examiner requires otherwise (and I can't imagine why that might be the case) obviously you keep the examiner happy for the exam.

(d) For cargo on seats, refer to CAO 20.16.2.5 and 6, in the first instance.

Thanks John. That's exactly what I have always told classes. It's high time CAO 20.7 was brought up to date. The difference between level and 1% slope can be almost 100kg on the Echo P Charts. Some people may consider that to be a significant difference. What bothers me is that in this day of computer exams, the student is presented with a data-entry box requiring the answer to be typed in. How much margin does the examiner give for the 'correct' answer?

I often find that the KDR for students who have scored over 90% in the CASA exam contains 'Use of Performance Charts' as a Question incorrectly answered. I can't understand why CASA hasn't made a clear statement on this.

There is a statement in the ECHO data provided with the exam, and in CAO 20.16.5.1.and 5.2, that says cargo may be placed on a control seat. It must be limited to 77kg and must be restrained (of course).

How much margin does the examiner give for the 'correct' answer?

Perhaps we should go have a cup or three of coffee with Gavin and get the answer from the proverbial ?

I can't understand why CASA hasn't made a clear statement on this.

The use of graphical data, in general, is pretty straightforward with the only real difficulty lying in the realm of "what constitutes appropriate accuracy" ? It has long been my view that the examiners ought to publish guidance material on this aspect of things so that the need for secret squirrel stuff is removed.

It must be limited to 77kg and must be restrained

As sideline points of interest - the 77kg comes from 170lb which is tied up with the old static design requirements for seats (TSO C39c/NAS 809). As I recall, the requirements for dynamic design look at a 50th percentile male dummy for the sled tests (AC 20-146A). There used to be an additional requirement for underseat baggage restraint - the airline 9kg limit relates to the old 20lb design requirement, although one sees some variations imposed by individual airlines. The really old static design required 6G forward restraint (DC3 -era) which then was increased to 9G. The present dynamic requirements relate to motor vehicle requirements and are in the vicinity of 20-odd G with some quite difficult requirements to ensure that the seat anchorages don't fail or pull out during the tests.

All getting a bit lost in the memory - in a previous life, I was heavily involved with aircraft seating design and certification but that was quite a while ago, now.

So far as restraint is concerned, ALL stuff has to be restrained. The minimum required forward g-factor is still 9G. For other directions, the loadings are a little different but the main one to remember is 9G forward.

Thank you both for your explanations! Appreciate it

Also one might ask the reasoning behind the requirement that cargo on a seat must be limited to 77kg, but it's OK to put a 120kg person on the same seat.

one might ask the reasoning

Indeed.

Certification is about putting lines in the sand to develop an acceptable set of conditions for design, testing and operation. Collectively, this process provides for an acceptably safe aircraft to roll out there into Industry use.

Not a perfectly safe aircraft, only acceptably.

There will be lots of situations where the design standards don't match the real world realities. One of these is that concern which Bob has identified - the design standards look at the 170lb occupant for the static case and 50th percentile for the dynamic. Those lines in the sand have to be put somewhere. As an aside, the 170lb goes back to a US North American statistical survey of army chaps in, as I recall, the 1940s.

It is important to keep in mind that the certification design standards don't give you any guarantees - it is all to do with probabilities.

If the occupant weighs less than the standard body, the seat will be stronger than the standard requires, if heavier, then weaker. Keep in mind that being lighter may not be better - the dynamic tests look at a maximum down spine load of, as I recall, 1530lb. The medical folks tell us that this is the sort of load the typical person can sustain without significant spinal injury. The lighter body may be subject to higher accelerations and a higher, more risky load than the standard considers. This is the reason that current helicopter seats, which have a very high downwards acceleration crash requirement, must incorporate a designed-in collapsing structure so that this maximum spine load is not exceeded. For the same reason, when you see the you beaut stunt car jumps in the movies, the driver will be in a similar collapsible seat structure for the landing impact sequence.

Likewise, if the forces imposed by a mishap significantly exceed the standard considerations, all bets are off. For instance, you may recall the flight test mishap on a GAF N24 Nomad at Avalon way back in 1976 - www.atsb.gov.au/publications/investigati.../aair/aair197603014/. The FTE on the flight, who was a very good mate of mine and an absolutely top bloke, survived but with major lower spine injuries. The impact loads greatly exceeded the (already quite high) envelope to which that seat was tested. Although it predated my time there, subsequently I was the design and certification engineer for the seat manufacturer for many years. The FTE's seat suffered a front beam compression failure and the failed structure caused his injuries during the impact sequence. Point of the tale is that, once again, there are no guarantees, only probabilities ...

What might this all have to do with Bob's seat loading question, you may ask ? While it would be a bit impractical to restrict occupants to a maximum weight, day in day out, we can do that for cargo - hence the double standard on this occasion, if you will.