This section of the FEDERAL REGISTER

contains regulatory documents having general

applicability and legal effect, most of which

are keyed to and codified in the Code of

Federal Regulations, which is published under

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REGISTER issue of each week.

Rules and Regulations Federal Register

14035 

Vol. 72, No. 57 

Monday, March 26, 2007 

DEPARTMENT OF TRANSPORTATION 

Federal Aviation Administration 

14 CFR Part 25 

[Docket No. NM357; Special Conditions No. 

25–347–SC] 

Special Conditions: Boeing Model 737– 

900ER series airplanes; Interaction of 

Systems and Structures 

AGENCY: Federal Aviation 

Administration (FAA), DOT. 

ACTION: Final special conditions. 

SUMMARY: This special condition is 

issued for the Boeing Model 737–900ER 

airplane. This airplane will have a novel 

or unusual design feature(s) associated 

with the interaction of systems and 

structures. The applicable airworthiness 

regulations do not contain adequate or 

appropriate safety standards for this 

design feature. This special condition 

contains the additional safety standards 

that the Administrator considers 

necessary to establish a level of safety 

equivalent to that established by the 

existing airworthiness standards. 

DATES: Effective Date: March 19, 2007. 

FOR FURTHER INFORMATION CONTACT: 

Todd Martin, Aerospace Engineer, 

Airframe/Cabin Safety Branch, ANM– 

115, Transport Airplane Directorate, 

Aircraft Certification Service, 1601 Lind 

Avenue SW., Renton, Washington 

98057–3356; telephone (425) 227–1178; 

facsimile (425) 227–1232; electronic 

mail Todd.Martin@faa.gov. 

SUPPLEMENTARY INFORMATION: 

Background 

On June 5, 2002, The Boeing 

Company, PO Box 3707, Seattle, 

Washington 98124, applied for an 

amendment to Type Certificate No. 

A16WE, to include the new Model 737– 

900ER. The Model 737–900ER, which is 

a derivative of the Model 737–900 

currently approved under A16WE, is a 

large transport airplane with two flight 

crew and the capacity to carry 215 

passengers. The airplane is powered by 

two CFMI CFM56–7 series turbofan 

engines. 

Type Certification Basis 

Under the provisions of § 21.101, 

Boeing must show that the Model 737– 

900ER meets the applicable provisions 

of 14 CFR part 25, as amended by 

Amendments 25–1 through 25–108, 

except for earlier amendments as agreed 

upon by the FAA. These regulations 

will be incorporated into the Type 

Certificate No. A16WE after type 

certification approval of the 737–900ER. 

In addition, the certification basis 

includes other regulations, special 

conditions and exemptions that are not 

relevant to this proposed special 

condition. Refer to Type Certificate No. 

A16WE for a complete description of 

the certification basis for this model 

airplane. 

If the Administrator finds that the 

applicable airworthiness regulations 

(i.e., 14 CFR part 25) do not contain 

adequate or appropriate safety standards 

for the Model 737–900ER because of a 

novel or unusual design feature, special 

conditions are prescribed under the 

provisions of § 21.16. 

In addition to the applicable 

airworthiness regulations and special 

conditions, the Model 737–900ER must 

comply with the fuel vent and exhaust 

emission requirements of 14 CFR part 

34 and the noise certification 

requirements of 14 CFR part 36. 

The FAA issues special conditions, as 

defined in § 11.19, they are published 

for comment under § 11.38, and they 

become part of the type certification 

basis under § 21.101. 

Special conditions are initially 

applicable to the model for which they 

are issued. Should the type certificate 

for that model be amended later to 

include any other model that 

incorporates the same or similar novel 

or unusual design feature, or should any 

other model already included on the 

same type certificate be modified to 

incorporate the same or similar novel or 

unusual design feature, the special 

conditions would also apply to the other 

model under § 21.101. 

Novel or Unusual Design Features 

The Model 737–900ER airplane will 

incorporate novel or unusual design 

features. This special condition 

addresses equipment that may affect the 

airplane’s structural performance, either 

directly or as a result of failure or 

malfunction. 

This proposed special condition is 

identical or nearly identical to those 

previously required for type 

certification of other Boeing airplane 

models. The special condition was 

derived initially from standardized 

requirements developed by the Aviation 

Rulemaking Advisory Committee 

(ARAC), comprised of representatives of 

the FAA, Europe’s Joint Aviation 

Authorities (now replaced by the 

European Aviation Safety Agency), and 

industry. 

Discussion 

In addition to the requirements of part 

25, subparts C and D, the following 

special condition applies: 

Interaction of Systems and Structures 

The Boeing Model 737–900ER is 

equipped with systems that may affect 

the airplane’s structural performance 

either directly or as a result of failure or 

malfunction. The effects of these 

systems on structural performance must 

be considered in the certification 

analysis. This analysis must include 

consideration of normal operation and 

of failure conditions with required 

structural strength levels related to the 

probability of occurrence. 

Discussion of Comments 

Notice of proposed special conditions 

No. 25–06–11–SC for Boeing Model 

737–900ER airplanes was published in 

the Federal Register on October 31, 

2006 (71 FR 63718). A combined set of 

comments was received from the United 

States Air Force and the United States 

Navy. 

As noted previously, special 

conditions are prescribed under the 

provisions of § 21.16 when current 

regulations ‘‘do not contain adequate or 

appropriate safety standards * * * 

because of a novel or unusual design 

feature.’’ 

For several decades, transport 

category airplanes have employed 

automatic and electronic flight control 

systems, including load alleviation 

systems, flutter suppression systems, 

and stability augmentation systems. 

Failures in any of these systems may 

affect how the airplane will respond to 

maneuver, gust, and high speed 

conditions. That is, the loads introduced 


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to the airplane may increase as a result 

of failures in these systems, or the 

flutter capability of the airplane may be 

reduced. 

Since current regulations do not 

specify design loads criteria, including 

a safety factor for system failures, a 

special condition is needed to address 

such failures. To address the effects of 

system failures on the structural and 

flutter capability of the airplane, the 

FAA developed a special condition, 

which has been applied in essentially 

the same form since 1989, and which is 

proposed for the Boeing Model 737–

900ER. 

Comment 1: The commenters 

recommended that the proposed special 

condition not be implemented as a 

general rule. 

FAA response: At this time we are not 

implementing the proposed special 

condition as a general rule. The 

‘‘Conclusion’’ section of the proposed 

special condition (No. 25–06–11–SC) 

states that ‘‘This action affects only 

certain novel or unusual design features 

on one model of airplane. It is not a rule 

of general applicability.’’ We are 

considering rulemaking to incorporate 

this special condition into 14 CFR part 

25. If we do propose changes to 14 CFR 

part 25 the public will have the 

opportunity to comment on that 

rulemaking action. We have not 

changed this special condition as a 

result of this comment. 

Comment 2: The commenters 

recommended that systems failures be 

addressed individually and that 

exceptions to existing standards and 

rules be reviewed on a case-by-case 

basis. 

FAA response: We do not agree with 

this recommendation. Although the 

proposed special condition allows the 

use of safety factors of less than 1.5, we 

do not regard this as an exception to the 

current regulation. The current CFR 

regulation does not specify design loads 

criteria, including a safety factor, for 

system failures. This is why special 

conditions are needed. We have not 

changed this special condition as a 

result of this comment. 

Comment 3: The commenters noted 

that Figure 1 in the proposed special 

condition, which is a plot of safety 

factor versus failure probability, shows 

that for failure occurrences more 

frequent than 10–5 per flight hour, the 

factor of safety is equal to 1.5 and 

cannot be reduced. However, the text of 

the proposed rule indicates in several 

places that this probability threshold is 

10–3. 

FAA response: We infer that the 

commenters are suggesting there are 

errors in the proposed special condition 

and that the text should be revised to 

change the 10–3 references to 10–5. We 

do not agree that the references to 10–3

in the text are errors. The three 

references to 10–3 in the text of the 

proposed special condition do not apply 

to Figure 1. The first two references to 

the 10–3 probability threshold are notes 

that apply only to Figures 2 and 3 of the 

proposed special condition. The third 

reference to 10–3 applies to subsequent 

failures following dispatch with a 

known failure. We have not changed 

this special condition as a result of this 

comment. 

Comment 4: The commenters are 

concerned that the definition of the term 

‘‘Qj = Probability of being in a failure 

condition,’’ is too vague and that the 

probability of being in a failure mode 

has to be more clearly defined to avoid 

potential loopholes. The term appears in 

the proposed special condition as 

follows: ‘‘Qj = Probability of being in a 

failure condition, which is defined as Pj

= Probability of failure occurrence 

multiplied by Tj = Average time spent 

in failure condition.’’ The concern is 

that an artificially low value of Tj would 

result in an inappropriate value of Qj. 

As an example, for a spoiler failure on 

landing approach, the Qj variable would 

be very small since you only spend a 

few minutes in that condition. 

FAA response: We believe that the 

definitions of probability and exposure 

time are sufficiently clear, and that their 

use is appropriate in this special 

condition. The term Tj applies to 

‘‘continuation of flight’’ failures, and 

thereby accounts for the maximum 

possible exposure period of the failure. 

If a failure is not detected, then Tj equals 

the average latency period for that 

failure mode. This results in a high 

value of Tj (potentially hundreds of 

hours), a high value of Qj, and little or 

no reduction of the safety factor. If the 

failure was detected, then its exposure 

would be limited and its effects 

mitigated by pilot actions. In this case, 

a reduced value of Qj and a 

corresponding reduced safety factor is 

appropriate. 

Comment 5: The commenters stated 

that the net effect of the proposed 

special condition would be a reduction 

in reliability when compared to the 

current practice for defining failure 

condition safety factors. The 

commenters also stated that the current 

practice has a historical track record of 

success. The commenters also noted 

that the allowed reduction of the safety 

factor is not analytically nor empirically 

justified. 

FAA response: We do not believe that 

this special condition reduces reliability 

or structural integrity when compared to 

the current practice for defining failure 

condition safety factors. The current 

regulation does not specify design loads 

criteria, including a safety factor, for 

system failures. Special conditions are 

needed to define these criteria. Also, the 

intent of this special condition has been 

applied for over ten years. Prior to this 

special condition we outlined similar 

criteria in Advisory Circular 25.672–1, 

Active Flight Controls, dated November 

15, 1983. 

While not analytically precise, we 

believe that reduced safety factors for 

low probability events are justified. 

Safety factors provide an additional 

margin above limit load capability. For 

low probability events, less margin is 

needed because these events will occur 

less often. For high probability events, 

more margin is needed, therefore, the 

full 1.5 safety factor is required. The 

relationship between the probability 

and the severity of a failure condition is 

similar to that used in a system safety 

assessment: High probability events 

must only have minor consequences, 

whereas low probability events may 

have major or hazardous consequences. 

In all cases, the objective is that no 

failure or combination of failures may 

be catastrophic. 

Comment 6: The commenters 

recommended that the process to be 

used to determine the reliability of a 

system be defined. The commenters also 

recommended that for each airplane 

model, the airframe manufacturer 

document all of the systems and 

structure subject to the proposed special 

conditions. 

FAA response: We believe that the 

process for determining the reliability of 

a system is well defined in this special 

condition because the special condition 

states that the failure condition and 

probabilistic terms are the same as those 

defined in § 25.1309, Equipment, 

systems, and installations. That 

regulation’s advisory material, Advisory 

Circular 25.1309–1A, System Design 

and Analysis, dated June 21, 1988, 

provides an acceptable process for 

determining the reliability of systems 

(that is, their probability of failure). 

We also note that as part of the 

certification process, airframe 

manufacturers are required to document 

the systems and structures subject to 

this special condition. 

Comment 7: The commenters stated 

that in Figure 3 of the proposed special 

condition, it is not clear how the flutter 

clearance speed should be determined 

when the probability of being in a 

failure condition, Qj, is between 1 and 

10–5. 

FAA response: Figure 3 of this special 

condition shows that when the 


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probability of being in the failure 

condition, Qj, is equal to one, the flutter 

clearance speed is V′′, which is the 

speed as defined by § 25.629(b)(1). (This 

is the same as the clearance speed with 

no failures.) When Qj = 10–5, the 

clearance speed is V′, which is the 

clearance speed with failures, as defined 

by § 25.629(b)(2). If Qj is between 1 and 

10–5, then the clearance speed varies 

linearly between V′′ and V′. This can be 

calculated as V = V′′ + 0.2(logQj)(V′′–V′). 

Comment 8: The commenters noted 

that the United States Air Force 

threshold for allowing a reduced 

clearance speed is 10–7 per flight hour. 

A note accompanying Figure 3 in the 

proposed special conditions indicates 

that the flutter clearance speed may not 

be less than V′′ if Pj is greater than 10–3

per flight hour. V′′ is the clearance speed 

with no failures, which includes a 15% 

margin on the design dive speed, VD/ 

MD. The commenters suggested that the 

10–7 per flight hour threshold is more 

appropriate than the 10–3 per flight hour 

threshold because the flutter analysis 

may inaccurately predict a critical 

flutter mechanism under a failed 

condition. The commenters also pointed 

out that failure conditions are not 

typically flutter tested in flight. 

FAA response: We believe that the 

flutter clearance speeds for failures are 

adequate as defined. Flutter clearance 

speeds for failure cases are defined in 

both § 25.629 and in these special 

conditions. The flutter clearance speed 

for failure cases defined in § 25.629 has 

not changed significantly since 

Amendment 25–0, issued in 1965. The 

service history on products certificated 

to Amendment 25–0, or later, has been 

acceptable regarding the effects of 

failures on flutter. The flutter clearance 

speed defined in these special 

conditions exceeds that defined in 

§ 25.629 (and is therefore more 

conservative) for all failure conditions 

whose probability is greater than 10–5. 

No changes were made to these 

special conditions as a result of these 

comments. The special conditions are 

adopted as proposed. 

Applicability 

As discussed above, this special 

condition is applicable to the Boeing 

Model 737–900ER. Should Boeing apply 

at a later date for a change to the type 

certificate to include another model 

incorporating the same novel or unusual 

design feature, this special condition 

would apply to that model as well. 

Effective Upon Issuance 

Under standard practice, the effective 

date of final special conditions would 

be 30 days after the date of publication 

in the Federal Register; however, as the 

certification date for the Boeing Model 

737–900ER is imminent, the FAA finds 

that good cause exists to make this 

special condition effective upon 

issuance. 

Conclusion 

This action affects only certain novel 

or unusual design features on one model 

of airplane. It is not a rule of general 

applicability. 

List of Subjects in 14 CFR Part 25 

Aircraft, Aviation safety, Reporting 

and recordkeeping requirements. 

The authority citation for these 

special conditions is as follows: 

Authority: 49 U.S.C. 106(g), 40113, 44701, 

44702, 44704. 

The Special Condition 

■ Accordingly, pursuant to the authority 

delegated to me by the Administrator, 

the following special conditions are 

issued as part of the type certification 

basis for Boeing Model 737–900ER 

airplanes. 

Interaction of Systems and Structures 

In addition to the requirements of part 

25, subparts C and D, the following 

proposed special condition would 

apply: 

a. For airplanes equipped with 

systems that affect structural 

performance—either directly or as a 

result of a failure or malfunction—the 

influence of these systems and their 

failure conditions must be taken into 

account when showing compliance with 

the requirements of part 25, subparts C 

and D. Paragraph b, below, must be used 

to evaluate the structural performance of 

airplanes equipped with these systems. 

b. Interaction of Systems and 

Structures. 

(1) General: The following criteria 

must be used for showing compliance 

with this special condition for 

interaction of systems and structures 

and with § 25.629 for airplanes 

equipped with flight control systems, 

autopilots, stability augmentation 

systems, load alleviation systems, flutter 

control systems, and fuel management 

systems. 

(a) The criteria defined herein address 

only the direct structural consequences 

of the system responses and 

performances. They cannot be 

considered in isolation but should be 

included in the overall safety evaluation 

of the airplane. These criteria may, in 

some instances, duplicate standards 

already established for this evaluation. 

These criteria are applicable only to 

structures whose failure could prevent 

continued safe flight and landing. 

Specific criteria that define acceptable 

limits on handling characteristics or 

stability requirements when operating 

in the system degraded or inoperative 

modes are not provided in this special 

condition. 

(b) Depending upon the specific 

characteristics of the airplane, 

additional studies may be required that 

go beyond the criteria provided in this 

special condition in order to 

demonstrate the capability of the 

airplane to meet other realistic 

conditions, such as alternative gust or 

maneuver descriptions for an airplane 

equipped with a load alleviation system. 

(c) The following definitions are 

applicable to this paragraph. 

Structural performance: Capability of 

the airplane to meet the structural 

requirements of part 25. 

Flight limitations: Limitations that 

can be applied to the airplane flight 

conditions following an in-flight 

occurrence and that are included in the 

flight manual (e.g., speed limitations 

and avoidance of severe weather 

conditions). 

Operational limitations: Limitations, 

including flight limitations, that can be 

applied to the airplane operating 

conditions before dispatch (e.g., fuel, 

payload, and Master Minimum 

Equipment List limitations). 

Probabilistic terms: The probabilistic 

terms (probable, improbable, and 

extremely improbable) used in this 

special conditions are the same as those 

used in § 25.1309. 

Failure condition: The term failure 

condition is the same as that used in 

§ 25.1309. However, this special 

condition applies only to system failure 

conditions that affect the structural 

performance of the airplane (e.g., system 

failure conditions that induce loads, 

change the response of the airplane to 

inputs such as gusts or pilot actions, or 

lower flutter margins). 

(2) Effects of Systems on Structures. 

(a) General. The following criteria 

will be used in determining the 

influence of a system and its failure 

conditions on the airplane structure. 

(b) System fully operative. With the 

system fully operative, the following 

apply: 

(1) Limit loads must be derived in all 

normal operating configurations of the 

system from all the limit conditions 

specified in subpart C (or used in lieu 

of those specified in subpart C), taking 

into account any special behavior of 

such a system or associated functions or 

any effect on the structural performance 

of the airplane that may occur up to the 

limit loads. In particular, any significant 

non-linearity (rate of displacement of 


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control surface, thresholds or any other 

system non-linearities) must be 

accounted for in a realistic or 

conservative way when deriving limit 

loads from limit conditions. 

(2) The airplane must meet the 

strength requirements of part 25 (static 

strength, residual strength), using the 

specified factors to derive ultimate loads 

from the limit loads defined above. The 

effect of non-linearities must be 

investigated beyond limit conditions to 

ensure that the behavior of the system 

presents no anomaly compared to the 

behavior below limit conditions. 

However, conditions beyond limit 

conditions need not be considered, 

when it can be shown that the airplane 

has design features that will not allow 

it to exceed those limit conditions. 

(3) The airplane must meet the 

aeroelastic stability requirements of 

§ 25.629. 

(c) System in the failure condition. 

For any system failure condition not 

shown to be extremely improbable, the 

following apply: 

(1) At the time of occurrence. Starting 

from 1g level flight conditions, a 

realistic scenario, including pilot 

corrective actions, must be established 

to determine the loads occurring at the 

time of failure and immediately after 

failure. 

(i) For static strength substantiation, 

these loads multiplied by an appropriate 

factor of safety that is related to the 

probability of occurrence of the failure 

are ultimate loads to be considered for 

design. The factor of safety (FS) is 

defined in Figure 1. 

(ii) For residual strength 

substantiation, the airplane must be able 

to withstand two thirds of the ultimate 

loads defined in paragraph (c)(1)(i) of 

this section. For pressurized cabins, 

these loads must be combined with the 

normal operating differential pressure. 

(iii) Freedom from aeroelastic 

instability must be shown up to the 

speeds defined in § 25.629(b)(2). For 

failure conditions that result in speed 

increases beyond VC/MC, freedom from 

aeroelastic instability must be shown to 

those increased speeds, so that the 

margins intended by § 25.629(b)(2) are 

maintained. 

(iv) Failures of the system that result 

in forced structural vibrations 

(oscillatory failures) must not produce 

loads that could result in detrimental 

deformation of primary structure. 

(2) For the continuation of the flight. 

For the airplane in the system failed 

state and considering any appropriate 

reconfiguration and flight limitations, 

the following apply: 

(i) The loads derived from the 

following conditions (or used in lieu of 

the following conditions) at speeds up 

to VC/MC or the speed limitation 

prescribed for the remainder of the 

flight must be determined: 

(A) the limit symmetrical 

maneuvering conditions specified in 

§§ 25.331 and in 25.345. 

(B) the limit gust and turbulence 

conditions specified in §§ 25.341 and in 

25.345. 

(C) the limit rolling conditions 

specified in § 25.349 and the limit 

unsymmetrical conditions specified in 

§§ 25.367 and 25.427(b) and (c). 

(D) the limit yaw maneuvering 

conditions specified in § 25.351. 

(E) the limit ground loading 

conditions specified in §§ 25.473 and 

25.491. 

(ii) For static strength substantiation, 

each part of the structure must be able 

to withstand the loads in paragraph 

(c)(2)(i) of this special condition 

multiplied by a factor of safety, 

depending on the probability of being in 

this failure state. The factor of safety is 

defined in Figure 2. 


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Qj = (Tj)(Pj) where: 

Tj = Average time spent in failure condition 

j (in hours) 

Pj = Probability of occurrence of failure mode 

j (per hour) 

Note: If Pj is greater than 10¥3 per flight 

hour, then a 1.5 factor of safety must be 

applied to all limit load conditions specified 

in subpart C. 

(iii) For residual strength 

substantiation, the airplane must be able 

to withstand two thirds of the ultimate 

loads defined in paragraph (c)(2)(ii). For 

pressurized cabins, these loads must be 

defined combined with the normal 

operating differential pressure. 

(iv) If the loads induced by the failure 

condition have a significant effect on 

fatigue or damage tolerance, then their 

effects must be taken into account. 

(v) Freedom from aeroelastic 

instability must be shown up to a speed 

determined from Figure 3. Flutter 

clearance speeds V′ and V′′ may be 

based on the speed limitation specified 

for the remainder of the flight, using the 

margins defined by § 25.629(b). 


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V′ = Clearance speed as defined by 

§ 25.629(b)(2). 

V′′ = Clearance speed as defined by 

§ 25.629(b)(1). 

Qj = (Tj)(Pj) where: 

Tj = Average time spent in failure condition 

j (in hours) 

Pj = Probability of occurrence of failure mode 

j (per hour) 

Note: If Pj is greater than 10¥3 per flight 

hour, then the flutter clearance speed must 

not be less than V′′. 

(vi) Freedom from aeroelastic 

instability must also be shown up to V′ 

in Figure 3 above for any probable 

system failure condition combined with 

any damage required or selected for 

investigation by § 25.571(b). 

(3) Consideration of certain failure 

conditions may be required by other 

sections of this Part, regardless of 

calculated system reliability. Where 

analysis shows the probability of these 

failure conditions to be less than 10¥9, 

criteria other than those specified in this 

paragraph may be used for structural 

substantiation to show continued safe 

flight and landing. 

(d) Warning considerations. For 

system failure detection and warning, 

the following apply: 

(1) The system must be checked for 

failure conditions, not extremely 

improbable, that degrade the structural 

capability below the level required by 

part 25 or significantly reduce the 

reliability of the remaining system. As 

far as reasonably practicable, the 

flightcrew must be made aware of these 

failures before flight. Certain elements 

of the control system, such as 

mechanical and hydraulic components, 

may use special periodic inspections, 

and electronic components may use 

daily checks in lieu of warning systems 

to achieve the objective of this 

requirement. These certification 

maintenance requirements must be 

limited to components the failures of 

which are not readily detectable by 

normal warning systems and where 

service history shows that inspections 

will provide an adequate level of safety. 

(2) The existence of any failure 

condition, not extremely improbable, 

during flight that could significantly 

affect the structural capability of the 

airplane and for which the associated 

reduction in airworthiness can be 

minimized by suitable flight limitations 

must be signaled to the flightcrew. For 

example, failure conditions that result 

in a factor of safety between the airplane 

strength and the loads of part 25, 

subpart C, below 1.25 or flutter margins 

below V′′ must be signaled to the crew 

during flight. 

(e) Dispatch with known failure 

conditions. If the airplane is to be 

dispatched in a known system failure 

condition that affects structural 

performance or affects the reliability of 

the remaining system to maintain 

structural performance, then the 

provisions of this Special Condition 

must be met, including the provisions of 

paragraph (b), for the dispatched 

condition and paragraph (c) for 

subsequent failures. Expected 

operational limitations may be taken 

into account in establishing Pj as the 

probability of failure occurrence for 

determining the safety margin in Figure 

1. Flight limitations and expected 

operational limitations may be taken 

into account in establishing Qj as the 

combined probability of being in the 

dispatched failure condition and the 

subsequent failure condition for the 

safety margins in Figures 2 and 3. These 

limitations must be such that the 

probability of being in this combined 

failure state and then subsequently 

encountering limit load conditions is 

extremely improbable. No reduction in 

these safety margins is allowed, if the 

subsequent system failure rate is greater 

than 1E–3 per flight hour. 

Issued in Renton, Washington, on March 

19, 2007. 

Ali Bahrami, 

Manager, Transport Airplane Directorate, 

Aircraft Certification Service. 

[FR Doc. E7–5508 Filed 3–23–07; 8:45 am] 

BILLING CODE 4910–13–C 


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