U.S. Department of Transportation

Docket Operations

West Building Ground Floor, Room W12--140

1200 New Jersey Avenue, SE.,

Washington, DC 20590

Subject: Petition for relief from the flight data recorder resolution
requirements of 14 CFR § 121.344(d),(e), and (f) (includes Part 121,
Appendix M).

Gentlemen/Madam,

In accordance with the provisions of Section 11.61 of the Federal
Aviation Regulations (FAR), the Regional Airline Association (RAA), on
behalf of its affected member airlines, petitions for exemption to
permit the use of the Embraer EMB-145 series airplane in operations
under 14 CFR part 121 with a flight data recorder system that does not
fully meet the data resolution requirements of 14 CFR § 121.344(d), (e),
and (f) (includes Part 121, Appendix M).

The RAA members currently in need of an exemption include American Eagle
Airlines, Inc., Chautauqua Airlines, Inc., ExpressJet Holdings, Inc.,
Mesa Airlines, Inc., and Trans States Airlines, Inc. To avoid the need
to request future exemptions for the fleet currently affected, we
petition for exemption for RAA members and "similarly situated Part 121
operators".

Our petition replaces a petition previously submitted by Embraer (Docket
Number FAA-2008-0329) and is similar in substance to a petition
submitted by another manufacturer (Docket Number FAA-2002-11705). The
Embraer petition requested relief for model-specific airplanes rather
than relief for operators to operate affected aircraft under the Part
121 operating rules, but the end result is the same.

RAA requests that publication of our petition in the Federal Register be
waived in accordance with Section 11.87. We note that the substantive
provisions of our petition are idential to the petition of Embraer that
was published in the Federal Register for public comment on April 9,
2008 and that no public comments were submitted. Therefore we view this
petition as not precedent setting since the reasons and conditions to
grant an exemption have been previously scrutinized by the public and
found to be noncontroversial in content.

Respectfully submitted,

REGIONAL AIRLINE ASSOCIATION

David Lotterer

Vice President -- Technical Services

Petition for Exemption

Summary

Petitioner:

The Regional Airline Association respectfully requests an exemption on
the behalf of the affected operators of the Embraer EMB-145 series
airplanes, including all models listed on Type Certificate Data Sheet
T00011AT

Sections of 14 CFR Affected: 14 CFR § 121.344(d), (e), and (f),

Description of Relief Sought: Exemption to permit the use of the Embraer
EMB-145 series airplane in operations under the cited regulations with a
flight data recorder system that does not fully meet the data resolution
requirements of 14 CFR §§ 121.344(d), (e), and (f) (includes Part 121,
Appendix M)..

[Statement of Issue and Text of Current Regulation from which Relief is
Sought]{.underline}

On behalf of our affected member operators, the Regional Airline
Association (RAA) requests an exemption to the flight data recorder
parameter resolution requirement contained in the following operating
regulations:

14 CFR § 121.344(d), (e), and (f), (includes Part 121, Appendix M).

The exemption would be limited to three parameters which do not meet the
resolution requirement of the applicable appendix but still provide
adequate performance to not adversely affect their accident or incident
investigative value.

The shortcomings in data resolution in the Embraer EMB-145 series
aircraft are similar to those that have been found in other type
designs. Those airplanes were granted relief from the requirements of
the applicable operating rule by an amendment to that regulation that
allows for a relaxed standard (data resolution requirement) to be
applied to those models.

14 CFR §121.344(d) states "For all turbine-engine powered transport
category airplanes that are manufactured after October 11,1991,\--

\(1\) The parameters listed in paragraph (a)(1) through (a)(34) of this
section must be recorded within the ranges, accuracies, resolutions, and
recording intervals specified in Appendix M of this part by August 20,
2001. Parameters listed in paragraphs (a)(12) through (a)(14) each may
be recorded from a single source."

The requirements of 14 CFR § 121.344 (e) are identical to §121.344(d)
except that the manufacture date is August 18, 2000, and the number of
required parameters is 57. 14 CFR § 121.344(f) is similar with a
manufacture date of August 19, 2002 and 88 parameters required.

Appendix M to 14 CFR part 121 provides a table listing the required
range, accuracy, sampling interval, and resolution for each of the
parameters required by 14 CFR §121.344(d), (e), and (f). The data from
the table pertinent to this petition are reproduced below.

  --------------- ---------- ----------- ---------- ------------ -------------------
  Parameter       Range      Accuracy    Seconds    Resolution   Remarks
                             (sensor     per                     
                             input)      sampling                
                                         interval                

  5\--Normal      -3g to +6g +/- 1% of   0.125      0.004g       
  acceleration               max range                           
  (Vertical)                 excluding                           
                             datum error                         
                             of +/-5%                            

  26\--Radio      -20 to     +/-2 ft or  1          1 ft +5%     For
  Altitude        2,500 ft   +/-3%                  above 500    autoland/category 3
                             Whichever              ft..         operations. Each
                             is Greater                          radio altimeter
                             Below 500                           should be recorded,
                             ft and                              but arranged so
                             +/-5% Above                         that at least one
                             500 ft                              is recorded each
                                                                 second.

  85---Trailing   Full Range +/-5%       2          0.5% of full Trailing edge flaps
  edge flap and                                     range.       and cockpit flap
  cockpit flap                                                   control position
  control                                                        may each be sampled
  position                                                       alternately at 4
                                                                 second intervals to
                                                                 provide a sample
                                                                 each 0.5 second.
  --------------- ---------- ----------- ---------- ------------ -------------------

# 

# Background

It was discovered that the digital flight data recorder (DFDR) system of
the EMB-145 series has anomalies where the system does not record some
of the required parameters at the required resolution.

The table below compares the required Appendix M performance and the
performance provided by the current DFDR system.

+----------------------+-----------------------+-----------------------+
| Parameter            | Required Resolution   | Actual Resolution     |
+----------------------+-----------------------+-----------------------+
| 5\--Normal           | 0.004g                | 0.009g (1 out of 5    |
| acceleration         |                       | samples may have a    |
|                      |                       | resolution of 0.013g) |
+----------------------+-----------------------+-----------------------+
| 26\--Radio Altitude  | 1 ft +5% above 500 ft | 2 feet throughout     |
|                      |                       | operational range.    |
|                      |                       | This parameter        |
|                      |                       | exceeds the           |
|                      |                       | requirement for       |
|                      |                       | altitudes above 500   |
|                      |                       | feet.                 |
+----------------------+-----------------------+-----------------------+
| 85---Trailing Edge   | 0.5% of full range    | same as MFD display   |
| Flap Position        |                       | (1 up to 4 degrees    |
|                      | (0.225 degrees)       | for certain flap      |
|                      |                       | values given the      |
|                      |                       | voltage range to flap |
|                      |                       | position correlation  |
|                      |                       | that has been         |
|                      |                       | implemented)          |
+----------------------+-----------------------+-----------------------+

# Level of Safety Provided

Three of the parameters do not meet the resolution requirements of the
applicable appendices, but the resolution provided is adequate to
provide the function and the level of safety intended by the applicable
regulations.

The performance of the existing configuration of the DFDR system is
adequate to provide sufficient data quality so that any investigation of
accident or incident will not be hampered. More detail explaining why
the resolution for each parameter provided by the current system is
sufficient to provide the data necessary for accident and incident
investigation is contained in Appendix A to this letter.

RAA notes that other manufacturers have been faced with similar problems
in the past and that the applicable appendices of the operating
regulations have been revised to incorporate exceptions to the
requirements for certain type designs that could not meet the
requirements but still provided performance adequate to maintain the
investigative value of the data. A list of some of these exceptions is
in the table below.

  ------------------- -------------- ---------------- -----------------------
  Aircraft            Parameter      Required         Actual Resolution
  Manufacturer                       Resolution       

  Boeing - B717       Normal         0.004g           0.005 g
                      acceleration                    

  Dassault F900C/F900 Normal         0.004g           0.007g
  EX                  acceleration                    

  Dassault F900C/F900 Radio Altitude 1 ft +5% above   1.25 ft
  EX                                 500 ft           

  Airbus - A330/A340  Flap Position  0.5% of full     1.05% (0.250º\>0.127º)
                                     range            
  ------------------- -------------- ---------------- -----------------------

These revisions were implemented in the form of footnotes to the tables
in the appendices to the operating regulations that provided for a
different performance standard specific to that aircraft model. This
petition would effectively do the same thing, but by means of an
exemption to the regulation rather than an amendment.

Considering the negligible additional value that would be provided by
full compliance to the requirements of 14 CFR §121.344(d), (e), and (f),
the level of safety provided by the current DFDR system in the EMB-145
series is adequate to meet the requirements of 14 CFR §11.81(e) .

[Cost Information]{.underline}

Embraer estimates the nonrecurring cost to develop the hardware software
changes necessary to increase the resolutions of the affected parameters
to be approximately \$5.3 million, including \$1.9 million to develop
the modification and an additional \$3.4 million to implement the
necessary modifications in the affected fleet.

The development cost is expensive because it will be necessary to
develop a new hardware configuration for the flight data acquisition
unit (FDAU) used to acquire and condition the sensor signals to make
them compatible with the DFDR. This hardware development cost is in
addition to the software development for the DFDR and the FDAU that
would be necessary to implement the increases in resolution to the meet
the requirements of the applicable regulations.

The modification costs are driven principally by the large size of the
affected fleet (more than 650 aircraft in the United States under Part
121 operating rules).

# Public Interest Information

Granting this exemption would be in the public interest for the
following reasons:

1.  The current configuration of the DFDR system in the EMB-145 series
    provides adequate data accuracy, resolution, and sampling rate so
    that a complete and efficient investigation of any incident or
    accident can be conducted. No impediment to safety would result from
    the grant of this exemption.

2.  Current EMB-145 operators have a significant size fleet currently in
    service. To require immediate compliance to 14 CFR §121.344 (d),
    (e), or (f), as applicable, would require those airplanes to be
    removed from service until the corrective action is developed. This
    would require the operators to cancel flights, disrupt schedules,
    and forego revenue that would severely injure the operators as well
    as impose inconvenience and potential lost-time cost to the
    traveling public. This action would be counter to the public
    interest

[Operating Outside the United States]{.underline}

Affected operators who would make use of this exemption operate their
airplanes outside the United States. ICAO Annex 6 has no standard that
specifies resolution requirements for DFDR systems. A note references
the Minimum Operational Performance Specifications (MOPS) document from
EUROCAE or equivalent document as a source of performance requirements,
but notes do not constitute a standard. There is no need for the FAA to
file a difference with ICAO for the granting of this petition.

[Affected Fleet]{.underline}

As previously indicated, this issue affects all Embraer Emb-145 aircraft
currently in service. Because the affected operators routinely change
their fleet composition, RAA requests the exemption be applicable to RAA
airline members and similarly situated Part 121 operators. This will
allow the FAA to avoid issuing repetitive exemptions each time an
affected airplane is operated by another Part 121 operator.

[Summary]{.underline}

The current configuration of the DFDR system in the EMB-145 series
provides adequate data accuracy, resolution, and sampling rate so that a
complete and efficient investigation of any incident or accident can be
conducted. No impediment to safety would result from the grant of this
exemption.

Current EMB-145 operators have a significant size fleet currently in
service. To require compliance to the existing standards of the
applicable operating rules would require those airplanes to be
extensively modified. Because the analytical value provided by modified
DFDRs would not be improved compared to the existing system, no public
benefit would be gained from this significant expense. Therefore there
is public benefit in the granting of this petition from the elimination
of unnecessary expense.

These factors provide sufficient evidence that granting this petition
for exemption would be in the public interest as required by 14 CFR
§11.81(d).

[Appendix A]{.underline}

This section will outline why the resolution provided is adequate to
support the intended function and to readily provide the data necessary
to aid investigations of accidents and incidents.

[Normal Acceleration]{.underline}

The principal need for the normal acceleration parameter is to allow
investigators to reconstruct the vertical flight path of the airplane
and to measure the acceleration forces applied to the airframe. For this
the 0.009g resolution is adequate because this allows an acceleration of
only 3.5 inches per second^2^ to be sensed. Inflight accelerations of
this magnitude are not significant in either flight path reconstruction
or the determination of the loads imposed on the structure. The
occasional resolution shift to 0.013g is leaves enough sensitivity to
not adversely affect the value of the data.

NTSB has commented in another docket that the resolution limits for the
three acceleration parameters (vertical, longitudinal and lateral
acceleration) are important to detect things like brake release and
departure from the paved runway surface. In the case of the EMB-145
fleet, the small mass of the airplane more than compensates for the
resolution reduction. The sensitivity provided is still greater than
that of a fully compliant DFDR system installed in a larger, wide-body
airplane with significantly greater mass.

![](media/image1.png){width="6.624305555555556in"
height="4.127777777777778in"}Since FDR system is not required to provide
more than 8 samples per second which allows analysis only up to 4 Hz,
there is no need for a greater resolution since the precision of the
values provided are far below this resolution. Below it is presented a
comparison of measurements provided by aircraft prototype flight test
instrumentation (40 Hz) and that which would be provided by the FDR (8
Hz).

![](media/image2.png){width="6.624305555555556in"
height="3.9291666666666667in"}

The high frequency components which would justify the high resolution
are not present on the measurements, since the frequency components are
limited to 4 Hz.

The present resolution is therefore compatible with low acquisition
sample rate, which is acceptable for the analysis of low frequency
events such as flight maneuvers. Landing impact analysis will require
statistic and / or simulation model analysis if a suitable sample rate
is not provided, which in this case does not depend on the resolution.

2.2 Precision of theoretical calculations

Based on the limit load factors involved on the critical events (\> 2g)
the precision provided by the FDR with resolution 0.004 g would be 0.2
%. This is excessive when compared with the precision of the theoretical
methods used on aircraft load calculations which is around 5 %. Example
below shows the comparison between theoretical and tested results for
landing loads where a variation of +/- 8 % was observed.

![](media/image3.wmf){width="6.072222222222222in" height="3.775in"}

[Radio Altitude]{.underline}

Radio altitude is used to determine the vertical trajectory of the
airplane when the airplane is operating close to the ground. During
approach the typical sink rate is about eight feet-per-second, with a
reduction in sink rate to typically about 2.5 feet-per-second during the
landing flare. The inability to resolve a one-foot-per-second sink rate
is not significant. At a true airspeed of 120 knots, a runway slope of
only 0.5% will induce a bias in the sink rate roughly equal to that. In
addition, Appendix M requires an accuracy of +/- two feet and a sampling
rate of one hertz. With such a slow sampling rate, the two foot
resolution provided is adequate to support the necessary accuracy.

[Trailing Edge Flap Position]{.underline}

The basic one-degree resolution provided is enough to determine any
aerodynamic effects or to determine flap system behavior. Near full flap
deflection, where flap deflection resolution is lower, the difference in
aerodynamic characteristics between the resolvable flap angles is
negligible.

During an incident or accident investigation based on the FDR data, the
Flap position parameter will be used to estimate the aerodynamic effect
of the Flap position on aircraft behavior or infer some aircraft system
response based on the system logic and on the system interdependency
with the Flap system.

The Flap position parameter resolution is not so critical to estimate
the aircraft dynamic behavior since this determination has some inherent
inaccuracy and therefore is not very sensitive to small variations of
flap angle, especially at the higher flap angles where the resolution is
the worst.

Concerning system response or mode changes based on flap angle, the
majority of the systems on the EMB-145 use flap handle position as the
system input, not flap position. The only system outside the Flap system
and the FDR that depends on the flap position signal is the Stall
Protection System. The SPS uses this signal to determine when the shaker
and the pusher may be activated during flight. The resolution of the SPS
is larger than the FDR so that The SPS system discretizes a 0 to 10V
analog signal from the FECU to digital values associated to the Flap
positions 0, 9, 18, 22 and 45 as described at the report 145-ST-31,
appendix A. The resolution of the SPS system is rougher than the FDR
parameter resolution.

Appendix M to Part 121 requires that the accuracy of the flap position
parameter be +/- 3 deg or ". . .as pilot's indicator." It is not clear
what benefit is to be gained by having a resolution of 0.5% of full
range if the accuracy only has to equal that of the indicator. At the
highest flap angles where the FDR angle resolution is the lowest, the
difference in aerodynamic characteristics (lift curve, maximum lift
coefficient, drag) between the minimum readable flap angles is
negligible.