Aviation Topic of the Week
By Michael Oxner,
December 14, 2003
This week's topic:
Aircraft Movement Surface Condition Reports
Completely in line with the season, we'll take a real world turn to runway
surface conditions. I have to admit, I hadn't yet heard them called by
the name used as the title this week, but apparently that's the official
name. I've heard "Runway Surface Condition" reports, abbreviated to "RSC",
and "Runway Condition Reports", abbreviated to "RCR", and a few others,
but not the official name. Funny what you pick up when you read.
Purpose of AMSCR
Description of Terms
When AMSCRs are Issued
Example
Purpose of AMSCR
The AIP, AIR 1.6.4, is our primary reference for this week's
topic. The AMSCR is intended to provide pilots with advance notice of runway
conditions. The format of the report is intended to give a plain
language description, allowing the pilot to get a picture of the
runway environment. As it's called, runway "contamination" can make a big
difference in how the aircraft handles, and can make the difference as to
whether a runway is even useable. Braking performance is affected to various
degrees by different types of runway contamination, as is an aircraft's
ability to handle crosswind components. Also, many people don't consider
the effects on take-off ability. Trained pilots in the real world will.
Read on.
Light aircraft generally don't have to consider it, since many runways
in use are very long, but larger aircraft must consider braking on take-off.
In the event of a rejected take-off, the aircraft must have enough runway
to abort without overrunning it. This is particularly important if snowbanks
are at the far end, or if there is soft turf beyond the runway. Rejecting
a take-off might occur whether an engine fails before V1, gauges give bad
readings on throttle up, or whatever. Runway contaminants affect the braking
ability here just as well as for arrivals. For example, on a bare and dry
runway, a jet may normally, considering runway slope, current temperature,
pressure and humidity, and winds, require 5,500 feet of runway to complete
a take-off roll to V1 and, using proper technique, come to complete stop.
A wet runway may increase that distance significantly, maybe upwards of 8,000
feet. Now put a little snow or slush into the picture and a pilot may not
be able to ensure a safe take-off on a given runway.
For the real world, I'll offer one recommendation when requesting runway
reports from ATS personnel. Don't call on GND frequency for the destination
airport when you're in the air. The problem is that many airports share
a common frequency for GND. For example, Halifax International uses 121.9,
and so did Saint John when the tower was open there a few years back. This
means that when an aircraft halfway between the two airports (100 NM apart)
called Saint John GND in the air at 14,000 feet, everyone on 121.9 at Halifax
heard this call. This ties up another airport's frequency unnecessarily.
If the report needed cannot be obtained from the ATC of FSS unit working your
flight, ask them for another frequency or call the TWR instead. At least the
TWR frequency is expected to be used for airborne aircraft, so the likelihood
of interfering with another unit on the same frequency is reduced, even
though it still exists depending on you distance from destination and your
altitude. If TWR is too busy to provide this for you, you may have to put
off your landing until you can get the information required. If at all practical,
you should try to find a runway report in NOTAMs before you leave.
Description of Terms
As mentioned earlier, this is intended to be a plain language report.
While the concepts are pretty much standardized, the descriptive terms
allow flexibility in order to provide a reasonable snapshot of what can
be expected.
The conditions typically considered when reporting runway conditions
include, but are not limited to, the following list:
- Bare and dry pavement
- Bare and wet pavement
- Frost cover
- Loose snow, and its depth
- Slush
- Snow drifts (snow cover uneven in depth)
- Compacted snow
- Ice
The contamination by any of the above listed terms is generally given
in terms of a percentage of cover. If a runway has received snowfall and
snow removal hasn't commenced, the report would be likely to include merely,
"100% snow covered, up to 4 inches in depth", or whatever the depth would
actually be. In the case of drifting where the surface is uneven in depth,
the deepest value is likely to be used. When snow removal has commenced,
the runway is generally first cleared to length, often leaving the edges
for a later period. This ensures the runway is useable with better conditions
where required most. If this is the case, the report will indicate the width
of the cleared "centerline", and it will also indicate the remaining portion
of the runway and the conditions there. See the examples below. One thing
I'll mention here, though, is that in such a case, there will often be little
hills of snow lining the edges of the cleared portion. These are called "windrows",
and are expressed with that term and their depth, if they exist. Occasionally,
a runway may be cleared in the central portion, but it may not be centered
on the runway. If more of the runway is cleared on one side of the centerline
than on the other, both sides will be described individually. For gravel
runways where reports are issued, it is common not only to report the surface
contamination, but also what underlies the surface. For example, they might
report "snow on top of ice".
When AMSCRs are Issued
A Notice to Airmen (NOTAM) is issued for a field whenever winter maintenance
is provided and any of the following runway conditions exists:
- Slush or wet snow on the runway;
- Loose snow exceeding a depth of 1/4";
- The runway is not cleared to full width. When the runway is partially
cleared the report will also include a description of the uncleared portion(s);
- The CRFI reading is 0.40 or less.
The last one, CRFI, is the Canadian Runway Friction Index, and I'll
go into that one next week in a separate topic.
Examples
The NOTAMs will be published with the location identifier, the term
"RSC" to identify the report, the report information, and the date-time
group. The standard format for the date-time group is 10 digits, beginning
with the last two digits of the year, and two digits for each month, day,
hour and minute. Just remember largest unit to smallest. The time, and the
date, will always be UTC. I mention this because UTC is ahead of all regions
in Canada, so a report late in the day might seem to have the wrong date.
For example, 0300z on the 08th day of the month UTC is actually 2200 EST
on the 07th. Here are some examples, right out of the AIP.
For paved runways:
- CYGK RSC ALL RWYS 100 PERCENT LOOSE SNOW 4 INS 0201190630. CLEARING
EXPECTED TO COMMENCE 0201191000
- CYFB RSC 17/35 100 PERCENT SNOW DRIFTS 3-4 INS 0201191050
- CYHZ RSC 06/24 160 FT CENTERLINE 40 PERCENT COMPACTED SNOW 60
PERCENT FROST REMAINDER 80 PERCENT LOOSE SNOW UP TO 4 IN 20 PERCENT FROST
SANDED 100 FT CENTERLINE 0202131240
- CYFB RSC CANCELED 0201191400
This one was not in the AIP. I made it up for the sake of an example:
- CYQM RSC RWY 11/29 120 FT CENTERLINE 10 PERCENT BARE AND DRY
30 PERCENT LOOSE SNOW UP TO 1 IN 20 PERCENT COMPACTED SNOW 40 PERCENT ICE
PATCHES WITH WINDROWS UP TO 8 INS REMAINDER 80 PERCENT SNOW DRIFTS UP TO
3 INS 20 PERCENT COMPACTED SNOW
For gravel runways:
- CYRB RSC 17T/35T 1/2 IN LOOSE SNOW ON TOP OF COMPACTED SNOW 0112190640
- CYRB RSC 17T/35T 100 PERCENT ICE COVERED 0112210740
- CYGW RSC 04/22 1 IN LOOSE SNOW ON TOP OF ICE 0112220630
The lack of punctuation, namely periods, does make these a little difficult
for the uninitiated to read, but you get used to them fairly quickly. Also,
taxiway and apron surfaces are generally reported when airports provide
winter maintenance, although ATS personnel may or may not have access to
that information.
A recent storm at home in Moncton, and a reader request, started this
topic. Next we'll move on to another winter consideration (CRFI). I'm reachable
at my regular e-mail, moxner@nbnet.nb.ca.
Thanks for taking the time to read!