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O 

U,S. Department 

of Transportation 

Federal Aviation 

Admlnlstratton 

Small Airplane Directorate 

901 Locust 

Kaneae City, MO €4106 

•^-fp' fC 

Mr. Kim Hackett 

DOA Administrator 

Cessna Aircraft Company 

One Cessna Boulevard 

Wichita, KS 67277-7704 

Dear Mr. Hackett; 

Wc are enclosing a grant of your petition submitted on November 4,2009, requesting an 

exemption with time-limited conditions from the requirements of 14 CFR part 23, 

§§ 23,1549(a), (b), and (c). The exemption allows Cessna to obtain a type certificate for the 

Cessna model 525C airplanes with the current design of the low pressure rotary group shaft 

speed (Nl) and interstage turbine temperature (TIT) indication, which provides conflicting 

color indications in certain operational regimes, The exemption permits type certification 

approval with the non-compliant type design for a limited time. If you have any questions, 

please contact Mr. Pete Rouse at the above address or call him on 816-329-4135, 

Sincerely, 

5l^2-Kim Smith 

Manager, Small Airplane Directorate 

Aircraft Certification Service 

Enclosure 
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DS'TOF'nAVSpTAli 

Exemption No. 9997 

UNITED STATES OF AMERICA 

DEPARTMENT OF TRANSPORTATION 

FEDERAL AVIATION ADMINISTRATION 

WASHINGTON, DC 20591 

In the matter of the petition of 

CESSNA AIRCRAFT COMPANY 

for an exemption from §§ 23.1549(a), 

(b), and (c) 

of Title 14, Code of 

Federal Regulations 

Regulatory Docket No. FAA-2009-1170 

GRANT OF EXEMPTION 

By letter dated November 04,2009, Mr. Kim Hackett, Cessna Aircraft Company, One 

Cessna Boulevard, P.O. Box 7704, Wichita, Kansas 67277-7704 petitioned for an exemption 

with time-limited conditions from §§ 23.1549(a), (b), and (c) of Title 14 of the Code of 

Federal Regulations (CFR) to permit type certification of the Cessna model 525C airplanes 

witliout oil pressure and temperature indications specified in the rule. The proposed 

exemption would permit relief firom the requirements for arrangement, visibility, and colors 

for tlie engine oil temperature and pressure indications for the model 525 C airplanes. The 

current design of the low pressure rotaiy group shaft speed (Nl) and interstage turbine 

temperamre (ITT) indication of the model 525C airplanes provides conflicting color 

indications in certain operational regimes. The proposed exemption, if granted, would permit 

type certification approval of the model 525C airplanes with this non-compliant type design 

for a limited time. 

Th« petitioner requests relief from the following regulation[s]: 

Sections 23.1549(a), (b), and (c), in pertinent part, require certain arrangement, 

visibility, and colors for Nl and ITT indications. 

Th« petitioner supports its request with the following information: 

Cessna Aircraft Company requests an exemption with time-limited conditions from 

the requirements of 14 CFR 23.1549(a), (b), and (c) for the model 525C to the extent 

necessary to allow type certification of the Cessna model 525C airplanes with the 

current Nl and ITT displays. As a condition for granting the requested time-limited 

exemption, Cessna Aircraft will design and certify engine Nl and ITT displays that are 
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compliant with the current FAA interpretation of 14 CFR § 23.1549(a), (b), and (c) 

within 15 months of the granting of this exemption. Cessna Aircraft will provide a 

service bulletin to all field aircraft after certifying the new display. 

14 CFR Reference 

14 CFR § 23.1549: Powerolant and auxiliary power unit insimmpntB 

For each required powerplant and auxiliary power unit instrument, as appropriate to 

the type of instruments-

(a) Each maximum and, if applicable, minimum safe operating limit must be marked 

with a red radial or a red line; 

(b) Each nonnal operating range must be marked with a green arc or green line, not 

extending beyond the maximum and minimum safe limits; 

(c) Each takeoff and precautionary range must be marked with a yellow arc or a yellow 

line 

Background 

The cunrent installation of the Rockwell Collins Proline 21 system on the model 525C 

airplane contains static warning bands for L and RNl and for L and R ITT. Similar 

installations are installed and certified on other part 23 Cessna airplanes including the 

models 525, 525A, and 525B that have incorporated the Collins Proline 21, 

The static warning bands for the engine Nl and ITT have considerable field 

experience; the model 525 airplanes which incorporate the Proline 21 system have 

over 426,000 flight hours, the model 525A has over 517,000 flight hours, and the 

model 525B has over 250,000 flight hours. This is approximately 1.2 million flight 

hours for this type of display. There have been no reports of issues in the field related 

to how the engine Nl or ITT are displayed. 

Nl Display Discussion: 

The current model 525C Nl indication is displayed on the Multifimction Display 

(MFD), which is centrally located on the instrument panel. The visibility and location 

of the Nl display is similar to other previously certified Citation aircraft, and has been 

evaluated during flight testing of the model 525C. The caution and warning Nl limits 

are transmitted by the Full Autliority Digital Electronic Control (FADEC) as listed in 

Table 1. 
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Table 1: FJ44-4A Nl Limits 

Nl Limits 

Max Steady State 

Max Permissible Transient 

Max Transient Duration 

Nl percent 

104.76 percent 

105.76 percent 

(120 Sec) 

The Nl display consists of an analog scale and digital display for each engine. Nl is 

displayed on a tape/pointer display as a percentage of rpm. The data is also displayed 

digitally below the Nl scale. The analog scale range is 10 percent to 110 percent with 

tick marks at 20,40, 60, 80, 85,90, 95,100,105, and 110 percent. Scaling is linear 

between 10 percent and 80 percent, and between 80 percent and 110 percent. The Nl 

digital display is a boxed digital readout below the Nl scale with a range of 0 percent 

to 120 percent and a resolution of 0.1 percent. 

As described below, the scale is static and will display the same marking during all 

engine operations. This scale marking consists of a red line at the Max Steady State 

Limit of 104.76 percent. (Refer to Figure 1,) 

As an alternative to this display, the red line for the scale could be drawn at the Max 

Transient Limit of 105.76 percent. This would then require an amber band to be 

drawn between 104.76 percent and 105.76 percent. Due to the small size of this amber 

band and the limited visibility on this scale, and due to the engine being an Nl 

FADEC controlled engine, which would require a failure of the FADEC system to 

ever reach an Nl of this value, Cessna decided to draw the red line at 104.76 percent. 

This choice results in a conservative display marking for Nl. 

The tape/pointer on the display will change colors based on the FADEC provided 

limits. 

Figures 1 through 4 show both the current and proposed Nl display configuration. 

These figures represent the operation of theNl displays for different operating 

conditions. Each figure is preceded by a discussion for the specific operating 

condition. 

For Nl speed below the Max Steady State Limit (refer to Figure 1); 

For both the current and proposed displays, the tape/pointer on the analog scale 

is colored white and the Nl digital display is colored green. 
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Current Display Proposed Display 

Figure 1: Nl below Max Steady State Limit 

For Nl speed between the Max Steady State Limit and the Max Transient Limit for 

less than 120 seconds (refer to Figure 2): 

For the current display, the tape/pointer and digital digits will turn amber and 

flash for five seconds and then go steady amber. 

For the proposed display, the tape/pointer and digital digits will turn red and 

flash for five seconds and then go steady red. 
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Curreiit Di splay Proposed Di spiay 

Figure 2: Nl between the Max Steady State Limit and the 

Max Transient Limit for less than 120 sec 

For Nl speed between the Max Steady State Limit and the Max Transient Limit for 

greater than 120 seconds (refer to Figure 3): 

For the current display, the tape/pointer and digital digits will turn red and flash 

for five seconds and then go steady red. 

For the proposed display, the tape/pointer and digital digits will remain red due 

to already having been turned red per above. 
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Current Di splay Proposed Di splay 

Figure 3: Nl between the Max Steady State Limit and the 

Max Transient Limit for greater than 120 sec 

For Nl speeds above the Max Transient Limit (refer to Figure 4): 

For both the current and proposed displays, the tape/pointer and digital digits 

will turn red and flash for five seconds and then go steady red. If the pointer, 

tape and digital display and have already turned red due to being in the 

transient zone for more than 120 seconds the pointer, tape and digital display 

will remain a steady red and not flash. 
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Current Display Proposed Display 

Figure 4: Nl above the Max Transient Limit 

ITT Display Discussion: 

The current model 525C ITT indication is displayed on the MFD, which is centrally 

located on the instrument panel. The visibility and location of the ITT display is 

similar to other previously certified Citation aircraft, and has been evaluated during 

flight testily of the model 525C. The caution and warning ITT Hmits are transmitted 

by the FADEC as listed in Table 2. 

Table 2: FJ44-4A ITT Limits 

ITT Limits 

Max Steady State Limit 

Transient Limit 1: 

Transient Limit 2: 

Engine Running 

835*C 

855*C (0 sec) 

855°C 

(Dual Engine - 5 min 

Single Engine - 10 min) 

Engine Starting 

840*"C 

1000^C(15sec) 

900°C (30 sec) 

The display of ITT consists of an analog scale and tape/pointer for the respective 

engine. The ITT tape/pointer only shows when ITT is above 100 ^C. Scale range is 

100 °C to 1,050 °C, with tick marks at 200, 400,600,650, 700,750, 800, 850, 900, 

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950, 1,000, and 1,050 *C. Four linear scale portions exist, with scaling change above 

600 "C, 800 °C, and changing again above 900 "C. 

As described below, the ITT limits are dynamic and will display different markings 

based on the engine state (run or starting) and based on the value of ITT. These 

markings change as required to meet the FADEC provided ITT limits as shown in 

Table 2. Additionally, tlie tape/pointer will change colors based on the FADEC 

provided limits. 

The following discussion provides details on the current ITT display with respect to 

the dynamic scale and the tape/pointer color operation. Due to the complexity of the 

ITT limitations with respect to various transient temperature and time limits, Cessna is 

not able to provide a proposal for a compliant display at this time. In addition, 

FAA/Cessna coordination is required before a proposal for display of ITT can be 

presented. However, Cessna Aircraft Company is committed to incorporation of a 

display compliant to the related regulations. 

ITT Display with Engines Running 

Figures 5 through 9 show the current ITT display configuration with engines in the nm 

mode. These figures represent the operation of the ITT displays for different operating 

cases. Where necessary, each figure is preceded by a discussion for the specific case. 

Note that for Cases 1-5, ITT display operation is discussed with respect to dual 

engine operation. For One Engine Inoperative (OEI) conditions, the ITT display 

operates the same except that the engine running transient limit is ten minutes instead 

of five as shown in Table 2. 

Case 1 - ITT below Max Steady State Limit (refer to Figure 5) 

Display Item 

Tape/Pointer 

Scale Markings 

Display Characteristic 

White 

Amber Band - 835°C to 855'C 

Red Line-855°C 
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Figure 5: ITT below Max Steady State Limit 

Case 2 - ITT between the Max Steady State Limit and the Transient Limit for less than 

three minutes (refer to Figure 6) 

For Cases 2 through 4, the FADEC is transmitting a dual engine operation 

transient time limit of five minutes. Since there are operating conditions when 

an engine may operate for a brief time in the cautionary range, Cessna does not 

immediately turn the tape/pointer to amber when operating between 835 'C 

and 855 "C. The tape/pointer will remain white for three minutes. After three 

minutes, the tape/pointer will then turn amber and flash for five seconds after 

wliich it stays amber. This allows the pilot to operate in the cautionary range if 

required due to hot day conditions but provides sufficient notification prior to 

exceeding the five minute transient limit for the pilot to take corrective action 

by reducing the throttle. This display philosophy is consistent with other 

model 525 series displays and eliminates the possibility of the distraction of a 

flashing amber ITT tape/pointer during takeoff, especially considering that a 

fiill five minutes of operation is allowed in this transient region. 
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Display Item 

Tape/Pointer 

Scale Markings 

Display Characteristic 

White 

Amber Band - 835°C to 855*C 

Red Line-855*C 

Figure 6: ITT between the Max Steady State Limit and the 

Transient Limit for less than three minutes 

Case 3 - ITT between the Max Steady State Limit and the Transient Limit for three to 

five minutes (refer to Figure 7) 

Display Item 

Tape/Pointer 

Scale Markings 

Display Characteristic 

Amber 

(Flashes for 5 sec then steady) 

Amber Band - 835°C to 855°C 

Red Line-85 5*C 

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Figure 7: ITT between the Max Steady State Limit and the 

Transient Limit for three to five minutes 

Case 4 ~ ITT between the Max Steady State Limit and the Transient Limit for greater 

than five minutes (refer to Figure 8) 

Display Item 

Tape/Pointer 

Scale Markings 

Display Characteristic 

Red 

(Flashes for 5 sec then steady) 

Amber Band - 835°C to 855*C 

Red Line-855X 

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Figure 8: ITT between the Max Steady State Limit and the 

Transient Limit for greater than five minutes 

Case 5 - ITT above the Transient Limit (refer to Figure 9) 

Display Item 

Tape/Pointer 

Scale Markings 

Display Characteristic 

Red 

(Flashes for five sec then 

steady)* 

Amber Band - 835 °C to 855 °C 

Red Line-855 °C 

* If the pointer and tape have already turned red due 

to being in the transient zone for more than five 

minutes, the pointer and tape display will remain a 

steady red and not flash. 

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Figure 9: ITT above the Transient Limit 

ITT Display during Engine Start: 

The ITT display with respect to scale markings and tape/pointer operation is the same 

as described above in the ITT Display with Engines Running Discussion section of 

this document. 

Figures 10 through 12 show the cvurent ITT display configurations with engines in the 

start mode as determined by the FADEC. These figures represent the operation of the 

ITT displays for different operating cases. 

Per the Airplane Flight Manual (AFM), the pilot is responsible for ensuring ITT limits 

are not exceeded. This philosophy is consistent with the rest of the model 525 series 

airplanes as well as Cessna airplanes certificated under the requirements of 14 CFR 

part 25, Cessna experience with the FJ44 Series engines in general, as well as with the 

FJ44-4A installed on the model 525C in particular, is that hot engine starts are very 

unusual and infrequent. 

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Case 6 - ITT at or below Max Steady State Starting Limit (refer to Figure 10) 

Display Item 

Tape/Pointer 

Scale Markings 

Display Characteristic 

White 

Amber Band - 835 °C to 855 "C 

Red Line-855 «C 

Red Triangle-1000 *C 

Figure 10: ITT at or below Max Steady State Starting Limit 

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Case 7 - ITT above Max Steady State Starting Limit (refer to Figure 11) 

Display Item 

Tape/Pointer 

Scale Markings 

Display Characteristic 

White 

Amber Band- 835 "C to 855 =C 

Red Line-855 °C 

Red Triangle-1000 °C 

Figure 11: ITT above Max Steady State Starting Limit for any Length of Time 

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Case 8 - ITT above Max Starting Transient Limit (refer to Figure 12) 

Display Item 

Tape/Pointer 

Scale Markings 

Display Characteristic 

Red 

(Flashes for five sec then steady) 

Amber Band - 835 ^C to 855 °C 

Red Line-855 *C 

Red Triangle-1000-^C 

Figure 12: ITT above Max Starting Transient Limit 

Petition 

Cessna Aircraft Company requests an exemption with time-limited conditions firom 

the requirements of 14 CFR § 23.1549(a), (b), and (c) for the model 525C for the 

engine Nl and ITT displays on the model 525C. This exemption would allow type 

certification of the Cessna model 525C airplanes with tlie current Nl and ITT displays, 

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while permitting adequate time to design and certify the proposed scale display in 

order to establish full compliance with the latest interpretation of the requirements of 

14 CFR § 23.1549(a), (b), and (c). 

As a condition for granting the requested exemption, Cessna Aircraft will design and 

certify engine Nl and ITT displays that are fiilly compliant vwth the latest 

interpretation of 14 CFR § 23.1549(a), (b), and (c) within 15 months of the granting of 

this exemption, 

The next scheduled version of the display software ftom Collins (v2.0) has a 

certification schedule for TSO receipt by end of year 2010. Due to current manpower 

constraints at Collins, it is not feasible to incorporate the new Nl and ITT displays 

prior to v2.0 without significantly delaying v2.0. Collins display software v2.0 is 

required for EAS A certification and any delay in EASA certification could result in 

significant financial penalties for Cessna Aircraft Company. 

Cessna Aircraft will provide a service bulletin to all model 525C field aircraft after 

certifying the new display 

Further, prior to the installation of the service bulletin to install the newNl and ITT 

displays, Cessna Aircraft will include notes in the Airplane Flight Manual (AFM) to 

help clarify the band and tape/pointer colors. The notes will be removed once the 

service bulletin is installed. The essence of the note will be to address the following 

item; the specific wording is to be agreed upon between Cessna and FAA as part of the 

AFM approval process. 

• The color bands on the vertical tape for Nl and ITT will not change to 

red as the transient duration limits expire even though the tapes will 

change color. 

Petitioner's Public Interest Statement 

Cessna Aircraft Company states that granting this exemption would be in the public 

interest for the following reasons. 

1. The F.T44-4A engine FADEC includes many safety features to prevent the 

engine from exceeding the Nl and ITT limits. These include the following: 

• Automatically reducing fuel flow as required during a start to actively 

limit ITT. 

• For engine speed above idle, the FADEC actively governs the Nl speed 

to the set Nl schedule. 

• The FADEC will shutdown the engine if it detects an Nl overspecd 

condition. 

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2. The current engine Nl display allows for safe operation of the engine within its 

operational limits as shown by the 1.2 million flight hours of similar displays 

on other model 525 series aircraft. The current display provides two visual 

cues that will alert the pilots that an engine Nl limit has been exceeded. 

• The tape/pointer for that engine will turn the appropriate warning color 

and flash for five seconds, 

• The digital readout for that engine will be displayed in the appropriate 

color, flashing for five seconds. 

3. The current engine ITT display allows for safe operation of the engine within 

its operational limits as shown by the 1.2 million flight hours of similar 

displays on other model 525 series aircraft. The current display provides two 

visual cues that will alert the pilots that an engine ITT limit has been exceeded. 

• The tape/pointer for that engine will tum the appropriate warning color 

flashing for five seconds. 

4. Similar engine Nl and ITT displays are currently in use on other model 525 

series aircraft models with over 1.2 million flight hours of field service 

experience. There have been no reports by the pilots of confusion in reading 

and understanding the engine Nl or ITT displays and no reports of engine 

damage caused by misinterpreting the engine Nl or ITT displays. Therefore 

field experience has shown that the current engine Nl and ITT displays do not 

cause a hazard to the aircraft. 

5. The denial of this petition for exemption would result in the delay of the 

certification of model 525C airplanes for approximately 15 months. Cessna 

would experience a loss of revenue of at least $140 million in 2010 and $120 

million in 2011 due to this delay. This could also result in numerous aircraft 

order cancellations increasing the financial loss significantly. This would also 

result in the loss of revenue for partners and suppliers and the potential need 

for workforce reductions, all of which would be counter to the public interest, 

6. Cessna's customers have made utilization plans based on the agreed upon 

delivery schedule of these airplanes. Delay in the delivery date due to the 

redesign and retrofit of the engine Nl and ITT displays would impose 

significant financial penalties upon our customers and their businesses without 

a commensurate safety benefit, which is also counter to the public interest. 

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Notice and Public Procedure Provided 

A summary of the petition was published on December 29, 2009 (74 FR 68914). No 

comments were received. 

The FAA's analysis is as follows: 

To obtain this exemption, the petitioner must show, as required by 14 CFR part 11, 

§§ 11.81(d) and 11.81 (e): "(1) the reasons why granting your request would be in the public 

interest; that is, how it would benefit the public as a whole, and (2) the reasons why granting 

the exemption would not adversely affect safety, or how the exemption would provide a level 

of safety at least equal to that provided by the rule from which you seek the exemption." 

The FAA has carefully reviewed the infoimation contained in the petitioner's request for 

exemption. 

The FAA agrees with the petitioner's request for the following reasons: 

1. The FJ44-4A engine FADEC includes many safety features to prevent the engine from 

exceeding the Nl and ITT limits. These include the following: 

a. Automatically reducing fuel flow as required during a start to actively limit 

ITT. 

b. For engine speed above idle, the FADEC actively governs the Nl speed to the 

setNl schedule. 

c. The FADEC will shutdown the engine if it detects an Nl overspeed condition. 

2. The current engine Nl display allows for safe operation of the engine within its 

operational limits as shown by the 1.2 million flight hours of similar displays on other 

model 525 series aircraft. The current display provides two visual cues that will alert 

the pilots that an engine Nl limit has been exceeded, 

a. The tape/pointer for that engine will turn the appropriate warning color and 

flash for five seconds, 

b. The digital readout for that engine will be displayed in the appropriate color, 

flashing for five seconds. 

3. The current engine ITT display allows for safe operation of the engine within its 

operational limits as shown by the 1,2 million flight hours of similar displays on other 

model 525 series aircraft. The current display provides two visual cues that will alert 

the pilots that an engine ITT limit has been exceeded. 

a. The tape/pointer for that engine will tum the appropriate warning color, 

flashing for five seconds. 

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b. Similar engine Nl and ITT displays arc currently in use on other model 525 

series aircraft models with over 1.2 million flight hours of field service 

experience. There have been no reports by the pilots of confusion in reading 

and understanding the engine Nl or ITT displays and no reports of engine 

damage caused by misinterpreting the engine Nl or ITT displays. Therefore 

field experience has shown that the current engine Nl and ITT displays do not 

cause a hazard to the aircraft. 

4. The denial of this petition for exemption would result in the delay of the certification 

of model 525C airplanes for approximately 15 months. The economic impact to 

Cessna Aircraft Corporation would be severe and result in significant reductions in 

Cessna's workforce. Additionally, the economic impact to Cessna's suppliers and 

customers would also be significant. 

The FAA's Decision 

In consideration of the foregoing, I find that a grant of exemption is in the public interest. 

Therefore, pursuant to the authority contained in 49 U.S.C, §§ 40113 and 44701, delegated to 

me by the Administrator, Cessna Aircraft Company is granted an exemption with time-limited 

conditions from §§ 23.1549(a), (b), and (c) to the extent necessary to allow type certification 

of the Cessna model 525C airplanes with low pressure rotary group shaft speed (Nl) and 

interstage turbine temperature (ITT) indications not in compliance with the requirements of 

§ § 23.1549(a), (b), and (c) as they relate to the arrangement, visibility, and colors. For the 

model 525C airplanes, this exemption is subject to the following conditions and limitations: 

Conditions and Limitations 

1. Cessna Aircraft Company must certify and incorporate into the production line 

requirements low pressure rotary group shaft speed (Nl) and intersts^e turbine 

temperature (ITT) indications fiJly compliant with the requirements of 

§§ 23.1549(a), (b), and (c), into the model 525C airplanes no later than April 30, 

2011. 

2. Cessna Aircraft Company must retrofit the model 525C airplanes delivered under 

the terms of the exemption with the new low pressure rotary group shaft speed (Nl) 

and interstage turbine temperature (ITT) indications described in Condition 1 above 

no later than April 30,2012. 

3. Until the incorporation of the changes required in the above Conditions 1 and 2 of 

this exemption have been completed, Cessna Aircraft Company add to the airplane 

flight manual (AFM) a description of the indications and their conflicting color 

guidance, and the necessary instructions for properly interpreting the requirements 

low pressure rotary group shaft speed (Nl) and interstage turbine temperature (ITT) 

indications. 

4. For airplanes subject to Condition 2 of this exemption, the operating limitations 

section of the airplane flight manual (AFM) must include the following statement: 

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"No person may operate this airplane after April 30,2012, unless the low 

pressure rotary group shaft speed (Nl) and interstage turbine temperature (ITT) 

indications have been modified in accordance with the temis of Exemption No. 

9997." 

This statement may be removed fix)m the AFM after the required modification has 

been made. 

This exemption terminates on April 30,2011, unless sooner superseded or rescinded. 

Issued in Kansas City, Missouri on January 26, 2010, 

John Colomy 

Acting Manager, Small Airplane Directorate 

Aircraft Certificacion Service 

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