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now are considered the norm in
commercial air travel. Earlier this week,
I read an article in which the trade association
representing the airlines justified
the per-service charging for bags
and blankets by comparing them to
hotels that charge customers for raiding
the mini-bar.
As in 2001, every time the airlines
open their collective mouths to whine
about the cost of providing the goods
and services airlines are supposed to
provide as a function of commercial air
transportation, it creates an opportunity
for us to promote the flexibility, security
and convenience of general aviation
flight.
It has been a great 100 months. Thank
you all for your help and support. I’m
looking forward to the next 100! q
If you have comments or questions
about this article, send e-mails to
avionicsnews@aea.net.
THE VIEW FROM WASHINGTON
Continued from page 17
Vereniging van Nederlandse Verkeersvliegers
Dutch Air Line Pilots Association
Position Paper 07 / 1
EHRD Dispatch Dry/Wet
Revision: 19th January 2009
This position paper represents the
opinion of the Dutch Air Line Pilots
Association based on IFALPA / ECA
policy, legislation, scientific research
and manufacturer guidelines and
recommendations.
Issue
This position paper discusses whether the porous runway surface structure of EHRD produces an
effectively dry braking action with moderate rainfall and whether EHRD can be considered dry for
dispatch purposes, except when heavy rain (+RA) if forecasted.
Certification
With JAR 25 Orange Paper 25/88/1 national variants of JAR 25 were removed and JAR 25X1591
Supplementary Performance Information was introduced requiring supplementary performance
information to be furnished by the manufacturer for operations on wet and contaminated runways.
The following definitions of dry, wet and contaminated runways were introduced:
Dry runway: A runway which is neither wet nor contaminated, including those runways which have
been specially prepared with grooves or a porous pavement and maintained to retain effectively dry
braking action even when moisture is present.
Wet runway: A runway which is well-soaked but without significant areas of standing water. A
runway is considered well soaked when there is sufficient moisture on the runway surface to cause it
to appear reflective.
In the course of a few certifications some discrepancies were noted between the theoretical
methods of the AMJ 25X1591 introduced at Change 13 and measured results. As a result Temporary
Guidance Material (TGM/25/04) “Performance Information for Take-Off from Wet Runways;
Information on Precipitation Drag”, which calls for limited test substantiation, was published.
As a result of various runway overruns following high speed rejected takeoffs the National
Transportation Safety Board (NTSB) published a Special Investigation Report 90/2 which has among
others resulted in the review of certification requirements. The proposals were contained in the
comparable FAA NPRM 93-8 and JAA NPA 25BDG-244 and introduced in FAR 25 Amendment 92 and
JAR 25 Change 15. The original proposal of NPRM 93-8 addressed wet runway performance by
assuming a maximum tire-to-ground braking coefficient equal to one half of that for a dry runway.
Public comments however, based on ESDU Data Item 71026, resulted in a more elaborate approach
to address wet runway performance. From these data, it is readily apparent that wet runway
stopping performance is significantly affected by many more variables than dry runway stopping
performance, such as ground speed, tire pressure, tire tread depth, runway surface texture, water
depth, brake wear and maximum brake torque capability and anti-skid efficiency. The new
certification requirements provide a maximum tire-to-ground friction coefficient as a function of tire
pressure and groundspeed to be used in determining the wet runway accelerate-stop distances. In
addition to these values the anti-skid efficiency has to be taken into account. For a properly tuned
anti-skid system the following efficiencies may be used: on-off 30%, quasi-modulating 50% and fullymodulating
80%. At the option of the manufacturer other values may be used as a result from flight
testing.
The FAA and JAA agreed that grooved and Porous Friction Course (PFC) runways can offer
substantial safety benefits in wet conditions and it was agreed that 70% of the dry runway braking
coefficient conservatively represents the stopping performance on properly designed, constructed,
and maintained grooved or PFC runways. At the option of the manufacturer stopping performance
must be based on either 70% dry or according to another set of maximum tire-to-ground friction
　
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