PPRuNe Forums - CAS on airspeed indicator

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Quote:

Originally Posted by dook (Post 10095476)

Mr Engineer,

I'll give Peter a call. He lives just up the road and is an ex-colleague of mine. The book publisher in the past has injected some typo errors which were not picked up by the preafrooder, of which I was one.

At the request of the publisher all print submissions were sent as Word documents.

Having written a few books myself, I fully understand and sympathise!

Quote:

preafrooder

:)

G

G. The coloured arcs on the ASI are not unique to Cessna and are sensibly used by many manufacturers to comply with FAA regulations in that they placard and place right in front of the pilot vital limitations such as flap limit, manoeuvring, VNE, stall and other speeds and on the twins much more. Having flown most Beech, Cessna and Piper SE and ME aircraft I have found the coloured arcs a great safety feature. You would be surprised how many of these aircraft regularly cruise high in the yellow arc and the owners still use them in air races and just as I predicted one twin owner bent his wings. The flight manuals for many older UK certified aircraft often refer the pilot to the BAFM or stick a placard up out if sight in the wing root.

Coloured arcs are near universal - the issue is whether they are referenced to IAS or CAS in my opinion.

G

G. Having checked a 1973 Turbo 310 POH (pre GAMA format) it states that the limitations are in KCAS as are the colour markings on the ASI. The speeds shown in the performance section for take off, climb and landing are KIAS. The cruise performance tables are of course KTAS.

On a Reims F406 the limitations are shown in a chart listing CAS and IAS and over the full range there are only two points where there is a maximum of 1k difference. The limitations and the ASI show only KIAS.

Many of the older singles and twins whose design originated in the 50s and 60s and were built by many different companies had very low normal operating range, flap and gear limitations that do provide problems in integrating with faster traffic patterns.

I was on duty when an operator who had a fleet of Aztec aircraft with some ASIs displaying mph and others Kt. An 80 mph approach to minima and go around led a stall and to 3 deaths. The pilot normally flew another one where the ASI was in knots. The CAA would not permit the operator to change all aircraft to a common standard. Reporting deaths to loved ones and business colleagues one after the other is not a task I would like to do again.