VOLUME 4 AIRCRAFT EQUIPMENT AND OPERATIONAL AUTHORIZATIONS
CHAPTER 5 AIR AMBULANCE OPERATIONS
Section 7 Helicopter Emergency Medical Services (HEMS) Use of the
Aviation Digital Data Service (ADDS) Experimental HEMS Tool
Helicopter emergency medical services (HEMS) operate in a demanding
environment. They provide an invaluable service to the public by providing
crucial, safe, and efficient transportation of critically ill and injured
patients to medical care facilities. While the contribution of HEMS is profound
as a component of the nation’s medical infrastructure, from an operational
standpoint, it is a commercial aviation activity performed by Federal Aviation
Administration (FAA) certificated air carrier operators. Operations, therefore,
must have the highest level of safety.
Data. A review of the commercial HEMS accidents from January 1998
through December 2004 revealed that controlled flight into terrain (CFIT),
inadvertent flight into inadvertent instrument meteorological conditions (IMC),
and lack of operational control were predominant factors in many accidents,
particularly at night and during low visibility conditions. Of the
27 fatal HEMS accidents, 21 occurred during night operations. Of the 21 night
accidents, 16 of the operations originated under visual flight rules (VFR); the
pilots inadvertently flew into IMC conditions, resulting in a CFIT accident.
HEMS Weather Summit.
In order to support avoidance of CFIT and loss of control (LOC)
accidents, the FAA, the HEMS industry and the University Center for Atmospheric
Research (UCAR) conducted a HEMS Weather Summit in early 2006. One of the
conclusions of the Summit was the absence of usable ceiling and visibility data
between reporting and forecasting stations. Often, HEMS operators conduct
entire HEMS flights in the area between such stations, with reliance on
off-course stations and area forecasts to make critical flight planning
decisions. One of the outputs of this Summit was a commitment to providing the
HEMS operating community access to information that might support better
weather decision making in visual flight rules (VFR) operations.
Accordingly, FAA asked UCAR’s Research Applications Laboratory (RAL) to
develop a tool as a part of the Aviation Digital Data Service (ADDS)
experimental Web site. This tool would provide access to “gridded” ceiling and
visibility assessment in areas between Aviation Routine Weather Report (METAR)
and terminal weather forecasts (TAF) reporting/forecasting sites.
Gridded Ceiling and Visibility Assessment.
This ceiling and visibility data are “assessments,” meaning they are
determinations of the ceiling and visibility that is likely to exist in the
grid block based on terrain influences, technical assessments, and observations
provided to software forecasting models that automatically generate the
graphical product. The user must understand that this weather product is not
a report of an observation or a forecast. It is an assessment of the
ceiling and visibility at the time chosen by the user and at the location of
the grid block(s).
In addition, this product has not completed a rigorous Flight Standards
operational suitability assessment. This assessment establishes the product
either as a primary weather product that meets all safety and regulatory
requirements (e.g., METAR or TAF) or as a supplementary weather product for
increased situation awareness. Until that assessment, the product currently is
The user should be aware that the ADDS HEMS Tool derives ceiling and
visibility by interpolating the nearest METAR data. This interpolation
process, in effect, “stretches” limited-area METAR observations across a
broader area between stations accounting for terrain effects on ceiling height.
The results are the likely conditions between METAR stations. A critical issue,
however, is that the reliability of the information generally degrades as
distance from a METAR site increases. Users should apply practical judgment
when considering the “likely” weather conditions that are remote from a METAR
site. To aid in this judgment, the product provides confidence fields that
integrate a variety of product quality factors. Accordingly, indications of a
“likely” weather condition that indicates a “No-Go” condition should strongly
influence the decisions of certificate holders authorized to use this product.
ADDS HEMS Tool. The ADDS HEMS Tool allows the user to identify gridded
weather assessments in 5 km x 5 km blocks. The weather data available
includes flight category, ceiling, visibility, radar, convection, icing,
temperature, relative humidity, and wind. Overlays on the graphical data
include wind barbs, METARs, Pilot Weather Report (PIREPs), Airmen’s
Meteorological Information (AIRMETs)/significant meteorological information
(SIGMETs), TAFs, VHF omnidirectional range station (VORs), state and county
boundaries, and a base map of terrain and cultural information.
This data became available effective November 1, 2006 on the
ADDS Experimental Site at
The site contains a tutorial as well as “frequently asked questions.”
In addition, you can find a technical report on the performance of this
ADDS HEMS Tool at http://www.avmet.com/
under the “Supplementary Weather Products” menu.
We consider taking the tutorial and reviewing the report as vital to
effectively using the Tool.
Operators may not use this tool in any way to support instrument flight
rules (IFR) operations. The only approved use of this ADDS HEMS Tool is in
VFR operations and then only in the context of supporting a “No-Go”
decision. Operators may not use the ADDA HEMS tool as the sole source for
decisions to “Go.” They may only use established primary products such as
METARs, TAFs, area forecasts, weather depiction charts, prognosis charts, etc.,
to make both “Go” and “No-Go” decisions. We have provided the following
If primary products, such as METARs, TAFs and area forecasts indicate a
proposed flight would encounter weather conditions worse than those required by
operations specifications (OpSpec) for VFR operations, and the ADDS HEMS Tool
indicates that conditions meet OpSpecs minimums, an operator cannot use the ADDS
HEMS Tool to support a “Go” decision not supported by primary products.
If the primary products indicate that an operator could complete a
flight in conditions at or above the OpSpec minimums, and the ADDS HEMS Tool
indicated weather lower than required along the route of flight, the ADDS HEMS
Tool can support a “No-Go” decision. This is particularly important since many
primary products (such as area forecasts) do not have the specificity to
identify highly localized low weather conditions. The ADDS HEMS Tool can
resolve assessments at the 5 km x 5 km grid level.
The following table reflects the relationship of the ADDS HEMS Tool to
primary weather products.
Table 4‑20, Comparison of Primary Weather
Products and the ADDS HEMS Tool
* Because the ADDS HEMS Tool is an
experimental product, we encourage operators to make a “No-Go” decision when
the tool indicates ceilings and/or visibilities below OpSpec minimums even when
primary products indicate acceptable weather conditions (condition 3
in Table 4‑20).
In cases where the tool supports an initial “No-Go” decision, depending
on the extent of the area of assessed low ceilings and/or visibilities, it may
also provide information that would support re-routing a flight to avoid
indicated hazardous ceiling and visibility conditions. In these cases, the
primary products, as well as the ADDS HEMS Tool would then both indicate
acceptable conditions along the re-routed flight path, meeting the criteria of
condition 2 in Table 4‑20.
In some cases, a certificate holder may choose to disregard the ADDS
HEMS Tool because of direct observations, pilot reports, or other data. Should
the certificate holder elect to operate, however, when the tool indicates
unacceptable conditions, knowledge of the tool’s assessment may increase the
pilot’s situational awareness and support more timely in‑flight decisions
to divert or land short if the pilot observes deteriorating conditions
in-flight. Delaying such in-flight decisions substantially increases the
potential for inadvertent instrument meteorological conditions (IMC)
encounters, with the resulting increased risk of a CFIT or LOC accident.
4-1003 INSPECTOR RESPONSIBILITY.
operations inspectors (POIs) should encourage operators to review the ADDS HEMS
Tool tutorial and the “frequently asked questions” on the Web site, and the
cited technical report of the product’s performance.
obtain approval to use the ADDS HEMS Tool, the certificate holder must provide
access to, and pilots and other personnel who will use the ADDS HEMS Tool must
review, the ADDS HEMS Tool tutorial and the technical performance report before
using the product.
reviewing this documentation and establishing the method to accomplish (B)
above, the certificate holder may request authorization to use the ADDS HEMS
Tool to support VFR flight operations under their OpSpecs. Accomplish this
authorization by amending existing OpSpec paragraph A010 by inserting the
following text in subparagraph (a) after the approved weather information
“The FAA has authorized the certificate holder to use the
experimental ADDS HEMS Tool to support VFR flight planning. The ADDS HEMS Tool
controls only in the negative (it is applicable only in the “No-Go” decision).
The certificate holder may not conduct flight operations based solely on an
indication by the ADDS HEMS Tool that safe conditions have been assessed along
the proposed route of flight.”
RESERVED. Paragraphs 4‑1004 through 4‑1010.