Part V - Airworthiness Manual Chapter 525 - Transport Category Aeroplanes

Canadian Aviation Regulations (CARs) 2017-2

Content last revised: 2009/06/30

Preamble

SUBCHAPTERS

  • A (525.1-525.2),
  • B (525.21-525.255),
  • C (525.301-525.581),
  • D (525.601-525.899),
  • E (525.901-525.1207),
  • F (525.1301-525.1461),
  • G (525.1501-525.1587)
  • H (525.1701-525.1733)

APPENDICES

A, B, C, D, E, F, G, H, I, J, L, M, N

(amended 2009/05/11; no previous version)

APPENDIX N

Fuel Tank Flammability Exposure and Reliability Analysis
(amended 2009/05/11; no previous version)

N525.1 General
(amended 2009/05/11; no previous version)
  1. (a) This appendix specifies the requirements for conducting fuel tank fleet average flammability exposure analyses required to meet 525.981(b) and AppendixM of this chapter. For fuel tanks installed in aluminum wings, a qualitative assessment is sufficient if it substantiates that the tank is a conventional unheated wing tank.
    (amended 2009/05/11; no previous version)

  2. (b) This appendix defines parameters affecting fuel tank flammability that must be used in performing the analysis. These include parameters that affect all aeroplanes within the fleet, such as a statistical distribution of ambient temperature, fuel flash point, flight lengths and aeroplane descent rate. Demonstration of compliance also requires application of factors specific to the aeroplane model being evaluated. Factors that need to be included are maximum range, cruise mach number, typical altitude where the aeroplane begins initial cruise phase of flight, fuel temperature during both ground and flight times and the performance of a flammability reduction means(FRM) if installed.
    (amended 2009/05/11; no previous version)

  3. (c) The following definitions, input variables, and data tables must be used in the program to determine fleet average flammability exposure for a specific aeroplane model.
    (amended 2009/05/11; no previous version)
     

N525.2 Definitions
(amended 2009/05/11; no previous version)
  1. (a) Bulk Average Fuel Temperature means the average fuel temperature within the fuel tank or different sections of the tank if the tank is subdivided by baffles or compartments.
    (amended 2009/05/11; no previous version)

  2. (b) Flammability Exposure Evaluation Time (FEET). The time from the start of preparing the aeroplane for flight, through the flight and landing, until all payload is unloaded, and all passengers and crew have disembarked. In the Monte Carlo program, the flight time is randomly selected from the Flight Length Distribution (Table2), the pre-flight times are provided as a function of the flight time, and the post-flight time is a constant 30minutes.
    (amended 2009/05/11; no previous version)

  3. (c) Flammable. With respect to a fluid or gas, flammable means susceptible to igniting readily or to exploding. A non-flammable ullage is one where the fuel-air vapour is too lean or too rich to burn or is inert as defined below. For the purposes of this appendix, a fuel tank that is not inert is considered flammable when the bulk average fuel temperature within the tank is within the flammable range for the fuel type being used. For any fuel tank that is subdivided into sections by baffles or compartments, the tank is considered flammable when the bulk average fuel temperature within any section of the tank, that is not inert, is within the flammable range for the fuel type being used.
    (amended 2009/05/11; no previous version)

  4. (d) Flash Point. The flash point of a flammable fluid means the lowest temperature at which the application of a flame to a heated sample causes the vapour to ignite momentarily, or ‘‘flash.’’ Table1 of this appendix provides the flash point for the standard fuel to be used in the analysis.
    (amended 2009/05/11; no previous version)

  5. (e) Fleet average flammability exposure is the percentage of the flammability exposure evaluation time(FEET) each fuel tank ullage is flammable for a fleet of an aeroplane type operating over the range of flight lengths in a world-wide range of environmental conditions and fuel properties as defined in this appendix.
    (amended 2009/05/11; no previous version)

  6. (f) Gaussian Distribution is another name for the normal distribution, a symmetrical frequency distribution having a precise mathematical formula relating the mean and standard deviation of the samples. Gaussian distributions yield bell-shaped frequency curves having a preponderance of values around the mean with progressively fewer observations as the curve extends outward.
    (amended 2009/05/11; no previous version)

  7. (g) Hazardous atmosphere. An atmosphere that may expose maintenance personnel, passengers or flight crew to the risk of death, incapacitation, impairment of ability to self-rescue (that is, ability to escape unaided from a confined space), injury, or acute illness.
    (amended 2009/05/11; no previous version)

  8. (h) Inert. For the purpose of this appendix, the tank is considered inert when the bulk average oxygen concentration within each compartment of the tank is 12percent or less from sea level up to 10,000feet altitude, then linearly increasing from 12percent at 10,000feet to 14.5percent at 40,000feet altitude, and extrapolated linearly above that altitude.
    (amended 2009/05/11; no previous version)

  9. (i) Inerting. A process where a non-combustible gas is introduced into the ullage of a fuel tank so that the ullage becomes non-flammable.
    (amended 2009/05/11; no previous version)

  10. (j) Monte Carlo Analysis. The analytical method that is specified in this appendix as the compliance means for assessing the fleet average flammability exposure time for a fuel tank.
    (amended 2009/05/11; no previous version)

  11. (k) Oxygen evolution occurs when oxygen dissolved in the fuel is released into the ullage as the pressure and temperature in the fuel tank are reduced.
    (amended 2009/05/11; no previous version)

  12. (l) Standard deviation is a statistical measure of the dispersion or variation in a distribution, equal to the square root of the arithmetic mean of the squares of the deviations from the arithmetic means.
    (amended 2009/05/11; no previous version)

  13. (m) Transport Effects. For purposes of this appendix, transport effects are the change in fuel vapor concentration in a fuel tank caused by low fuel conditions and fuel condensation and vaporization.
    (amended 2009/05/11; no previous version)

  14. (n) Ullage. The volume within the fuel tank not occupied by liquid fuel.
    (amended 2009/05/11; no previous version)

N525.3 Fuel Tank Flammability Exposure Analysis
(amended 2009/05/11; no previous version)
  1. (a) A flammability exposure analysis must be conducted for the fuel tank under evaluation to determine fleet average flammability exposure for the aeroplane and fuel types under evaluation. For fuel tanks that are subdivided by baffles or compartments, an analysis must be performed either for each section of the tank, or for the section of the tank having the highest flammability exposure. Consideration of transport effects is not allowed in the analysis. The analysis must be done in accordance with the methods and procedures set forth in the Fuel Tank Flammability Assessment Method User’s Manual, dated May2008, document number DOT/FAA/AR–05/8. The parameters specified in N525.3(b) and(c) of this appendix must be used in the fuel tank flammability exposure “MonteCarlo” analysis.
    (amended 2009/05/11; no previous version)

  2. (b) The following parameters are defined in the MonteCarlo analysis and provided inN525.4 of this appendix:
    (amended 2009/05/11; no previous version)

    1. (1) Cruise Ambient Temperature, as defined in this appendix.
      (amended 2009/05/11; no previous version)

    2. (2) Ground Ambient Temperature, as defined in this appendix.
      (amended 2009/05/11; no previous version)

    3. (3) Fuel Flash Point, as defined in this appendix.
      (amended 2009/05/11; no previous version)

    4. (4) Flight Length Distribution, as defined in Table2 of this appendix.
      (amended 2009/05/11; no previous version)

    5. (5) Aeroplane Climb and Descent Profiles, as defined in the Fuel Tank Flammability Assessment Method User’s Manual, dated May2008, document number DOT/FAA/AR–05/8.
      (amended 2009/05/11; no previous version)

  3. (c) Parameters that are specific to the particular aeroplane model under evaluation that must be provided as inputs to the MonteCarlo analysis are:
    (amended 2009/05/11; no previous version)

    1. (1) Aeroplane cruise altitude.
      (amended 2009/05/11; no previous version)

    2. (2) Fuel tank quantities. If fuel quantity affects fuel tank flammability, inputs to the MonteCarlo analysis must be provided that represent the actual fuel quantity within the fuel tank or compartment of the fuel tank throughout each of the flights being evaluated. Input values for this data must be obtained from ground and flight test data or the approved fuel management procedures.
      (amended 2009/05/11; no previous version)

    3. (3) Aeroplane cruise mach number.
      (amended 2009/05/11; no previous version)

    4. (4) Aeroplane maximum range.
      (amended 2009/05/11; no previous version)

    5. (5) Fuel tank thermal characteristics. If fuel temperature affects fuel tank flammability, inputs to the MonteCarlo analysis must be provided that represent the actual bulk average fuel temperature within the fuel tank at each point in time throughout each of the flights being evaluated. For fuel tanks that are subdivided by baffles or compartments, bulk average fuel temperature inputs must be provided for each section of the tank. Input values for these data must be obtained from ground and flight test data or a thermal model of the tank that has been validated by ground and flight test data.
      (amended 2009/05/11; no previous version)

    6. (6) Maximum aeroplane operating temperature limit, as defined by any limitations in the aeroplane flight manual.
      (amended 2009/05/11; no previous version)

    7. (7) Aeroplane Utilization. The applicant must provide data supporting the number of flights per day and the number of hours per flight for the specific aeroplane model under evaluation. If there is no existing aeroplane fleet data to support the aeroplane being evaluated, the applicant must provide substantiation that the number of flights per day and the number of hours per flight for that aeroplane model is consistent with the existing fleet data they propose to use.
      (amended 2009/05/11; no previous version)

  4. (d) Fuel Tank FRM Model. If FRM is used, an approved MonteCarlo program must be used to show compliance with the flammability requirements of 525.981 and AppendixM of this chapter. The program must determine the time periods during each flight phase when the fuel tank or compartment with the FRM would be flammable. The following factors must be considered in establishing these time periods:
    (amended 2009/05/11; no previous version)

    1. (1) Any time periods throughout the flammability exposure evaluation time and under the full range of expected operating conditions, when the FRM is operating properly but fails to maintain a non-flammable fuel tank because of the effects of the fuel tank vent system or other causes;
      (amended 2009/05/11; no previous version)

    2. (2) If dispatch with the system inoperative under the Master Minimum Equipment List(MMEL) is requested, the time period assumed in the reliability analysis (60flight hours must be used for a 10-day MMEL dispatch limit unless an alternative period has been approved by the Minister);
      (amended 2009/05/11; no previous version)

    3. (3) Frequency and duration of time periods of FRM inoperability, substantiated by test or analysis acceptable to the Minister, caused by latent or known failures, including aeroplane system shut-downs and failures that could cause the FRM to shut down or become inoperative.
      (amended 2009/05/11; no previous version)

    4. (4) Effects of failures of the FRM that could increase the flammability exposure of the fuel tank.
      (amended 2009/05/11; no previous version)

    5. (5) If an FRM is used that is affected by oxygen concentrations in the fuel tank, the time periods when oxygen evolution from the fuel results in the fuel tank or compartment exceeding the inert level. The applicant must include any times when oxygen evolution from the fuel in the tank or compartment under evaluation would result in a flammable fuel tank. The oxygen evolution rate that must be used is defined in the Fuel Tank Flammability Assessment Method User’s Manual, dated May2008, document number DOT/FAA/AR–05/8.
      (amended 2009/05/11; no previous version)

    6. (6) If an inerting system FRM is used, the effects of any air that may enter the fuel tank following the last flight of the day due to changes in ambient temperature, as defined in Table4, during a 12-hour overnight period.
      (amended 2009/05/11; no previous version)

  5. (e) The applicant must submit for approval the fuel tank flammability analysis, including the aeroplane-specific parameters identified underN525.3(c) of this appendix and any deviations from the parameters identified in N525.3(b) of this appendix that affect flammability exposure, substantiating data and any airworthiness limitations and other conditions assumed in the analysis.
    (amended 2009/05/11; no previous version)

N525.4 Variables and Data Tables
(amended 2009/05/11; no previous version)

The following data must be used when conducting a flammability exposure analysis to determine the fleet average flammability exposure. Variables used to calculate fleet flammability exposure must include atmospheric ambient temperatures, flight length, flammability exposure evaluation time, fuel flash point, thermal characteristics of the fuel tank, overnight temperature drop and oxygen evolution from the fuel into the ullage.
(amended 2009/05/11; no previous version)

  1. (a) Atmospheric Ambient Temperatures and Fuel Properties.
    (amended 2009/05/11; no previous version)

      1. (1) In order to predict flammability exposure during a given flight, the variation of ground ambient temperatures, cruise ambient temperatures and a method to compute the transition from ground to cruise and back again must be used. The variation of the ground and cruise ambient temperatures and the flash point of the fuel is defined by a Gaussian curve, given by the 50percent value and a ±1-standard deviation value.
        (amended 2009/05/11; no previous version)

      2. (2) Ambient Temperature: Under the program, the ground and cruise ambient temperatures are linked by a set of assumptions on the atmosphere. The temperature varies with altitude following the International Standard Atmosphere(ISA) rate of change from the ground ambient temperature until the cruise temperature for the flight is reached. Above this altitude, the ambient temperature is fixed at the cruise ambient temperature. This results in a variation in the upper atmospheric temperature. For cold days, an inversion is applied up to 10,000feet, and then the ISA rate of change is used.
        (amended 2009/05/11; no previous version)

      3. (3) Fuel properties:
        (amended 2009/05/11; no previous version)

          1. (i) For Jet A fuel, the variation of flash point of the fuel is defined by a Gaussian curve, given by the 50percent value and a ±1-standard deviation, as shown in Table1 of this appendix. (amended 2009/05/11; no previous version)

          2. (ii) The flammability envelope of the fuel that must be used for the flammability exposure analysis is a function of the flash point of the fuel selected by the Monte Carlo for a given flight. The flammability envelope for the fuel is defined by the upper flammability limit(UFL) and lower flammability limit(LFL) as follows:
            (amended 2009/05/11; no previous version)

              1. (A) LFL at sea level = flash point temperature of the fuel at sea level minus10°F. LFL decreases from sea level value with increasing altitude at a rate of 1°F per 808feet.
                (amended 2009/05/11; no previous version)

              2. (B) UFL at sea level = flash point temperature of the fuel at sea level plus63.5°F. UFL decreases from the sea level value with increasing altitude at a rate of 1°F per 512feet.
                (amended 2009/05/11; no previous version)

              3. (4) For each flight analyzed, a separate random number must be generated for each of the three parameters (ground ambient temperature, cruise ambient temperature, and fuel flash point) using the Gaussian distribution defined in Table 1 of this appendix.
                (amended 2009/05/11; no previous version)

Table 1 — Gaussian Distribution for Ground Ambient Temperature, Cruise Ambient Temperature and Fuel Flash Point
(amended 2009/05/11; no previous version)

Parameter Temperature in °F
Ground ambient temperature Cruise ambient temperature Fuel flash point (FP)
Mean Temp
Neg1stddev
Pos 1 std dev
59.95
20.14
17.28
-70
8
8
120
8
8
  1. (b) The Flight Length Distribution defined in Table2 must be used in the MonteCarlo analysis.
    (amended 2009/05/11; no previous version)

Table 2 — Flight Length Distribution
(amended 2009/05/11; no previous version)

Flight length (NM) Aeroplane maximum range—nautical miles (NM)
From To 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000
  Distribution of flight lengths (percentage of total)
0 200 11.7 7.5 6.2 5.5 4.7 4.0 3.4 3.0 2.6 2.3
200 400 27.3 19.9 17.0 15.2 13.2 11.4 9.7 8.5 7.5 6.7
400 600 46.3 40.0 35.7 32.6 28.5 24.9 21.2 18.7 16.4 14.8
600 800 10.3 11.6 11.0 10.2 9.1 8.0 6.9 6.1 5.4 4.8
800 1000 4.4 8.5 8.6 8.2 7.4 6.6 5.7 5.0 4.5 4.0
1000 1200 0.0 4.8 5.3 5.3 4.8 4.3 3.8 3.3 3.0 2.7
1200 1400 0.0 3.6 4.4 4.5 4.2 3.8 3.3 3.0 2.7 2.4
1400 1600 0.0 2.2 3.3 3.5 3.3 3.1 2.7 2.4 2.2 2.0
1600 1800 0.0 1.2 2.3 2.6 2.5 2.4 2.1 1.9 1.7 1.6
1800 2000 0.0 0.7 2.2 2.6 2.6 2.5 2.2 2.0 1.8 1.7
2000 2200 0.0 0.0 1.6 2.1 2.2 2.1 1.9 1.7 1.6 1.4
2200 2400 0.0 0.0 1.1 1.6 1.7 1.7 1.6 1.4 1.3 1.2
2400 2600 0.0 0.0 0.7 1.2 1.4 1.4 1.3 1.2 1.1 1.0
2600 2800 0.0 0.0 0.4 0.9 1.0 1.1 1.0 0.9 0.9 0.8
2800 3000 0.0 0.0 0.2 0.6 0.7 0.8 0.7 0.7 0.6 0.6
3000 3200 0.0 0.0 0.0 0.6 0.8 0.8 0.8 0.8 0.7 0.7
3200 3400 0.0 0.0 0.0 0.7 1.1 1.2 1.2 1.1 1.1 1.0
3400 3600 0.0 0.0 0.0 0.7 1.3 1.6 1.6 1.5 1.5 1.4
3600 3800 0.0 0.0 0.0 0.9 2.2 2.7 2.8 2.7 2.6 2.5
3800 4000 0.0 0.0 0.0 0.5 2.0 2.6 2.8 2.8 2.7 2.6
4000 4200 0.0 0.0 0.0 0.0 2.1 3.0 3.2 3.3 3.2 3.1
4200 4400 0.0 0.0 0.0 0.0 1.4 2.2 2.5 2.6 2.6 2.5
4400 4600 0.0 0.0 0.0 0.0 1.0 2.0 2.3 2.5 2.5 2.4
4600 4800 0.0 0.0 0.0 0.0 0.6 1.5 1.8 2.0 2.0 2.0
4800 5000 0.0 0.0 0.0 0.0 0.2 1.0 1.4 1.5 1.6 1.5
5000 5200 0.0 0.0 0.0 0.0 0.0 0.8 1.1 1.3 1.3 1.3
5200 5400 0.0 0.0 0.0 0.0 0.0 0.8 1.2 1.5 1.6 1.6
5400 5600 0.0 0.0 0.0 0.0 0.0 0.9 1.7 2.1 2.2 2.3
5600 5800 0.0 0.0 0.0 0.0 0.0 0.6 1.6 2.2 2.4 2.5
5800 6000 0.0 0.0 0.0 0.0 0.0 0.2 1.8 2.4 2.8 2.9
6000 6200 0.0 0.0 0.0 0.0 0.0 0.0 1.7 2.6 3.1 3.3
6200 6400 0.0 0.0 0.0 0.0 0.0 0.0 1.4 2.4 2.9 3.1
6400 6600 0.0 0.0 0.0 0.0 0.0 0.0 0.9 1.8 2.2 2.5
6600 6800 0.0 0.0 0.0 0.0 0.0 0.0 0.5 1.2 1.6 1.9
6800 7000 0.0 0.0 0.0 0.0 0.0 0.0 0.2 0.8 1.1 1.3
7000 7200 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.4 0.7 0.8
7200 7400 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.3 0.5 0.7
7400 7600 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.2 0.5 0.6
7600 7800 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.1 0.5 0.7
7800 8000 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.1 0.6 0.8
8000 8200 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.5 0.8
8200 8400 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.5 1.0
8400 8600 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.6 1.3
8600 8800 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.4 1.1
8800 9000 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.2 0.8
9000 9200 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.5
9200 9400 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.2
9400 9400 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.1
9600 9600 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.1
9800 9800 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.1
  1. (c) Overnight Temperature Drop. For aeroplanes on which FRM is installed, the overnight temperature drop for this appendix is defined using:
    (amended 2009/05/11; no previous version)

      1. (1) A temperature at the beginning of the overnight period that equals the landing temperature of the previous flight that is a random value based on a Gaussian distribution; and
        (amended 2009/05/11; no previous version)

      2. (2) An overnight temperature drop that is a random value based on a Gaussian distribution.
        (amended 2009/05/11; no previous version)

      3. (3) For any flight that will end with an overnight ground period (one flight per day out of an average number of flights per day, depending on utilization of the particular aeroplane model being evaluated), the landing outside air temperature(OAT) is to be chosen as a random value from the following Gaussian curve:
        (amended 2009/05/11; no previous version)

Table 3 — Landing Outside Air Temperature
(amended 2009/05/11; no previous version)

Parameter Landing outside air temperature°F
Mean Temperature
negative 1 std dev
positive 1 std dev
58.68
20.55
13.21
      1. (4) The outside ambient air temperature(OAT) overnight temperature drop is to be chosen as a random value from the following Gaussian curve:

Table 4 — Outside Air Temperature (OAT) Drop
(amended 2009/05/11; no previous version)

Parameter OAT drop temperature°F
Mean Temperature
1 std dev
12.0
6.0
  1. (d) Number of Simulated Flights Required in Analysis. In order for the MonteCarlo analysis to be valid for showing compliance with the fleet average and warm day flammability exposure requirements, the applicant must run the analysis for a minimum number of flights to ensure that the fleet average and warm day flammability exposure for the fuel tank under evaluation meets the applicable flammability limits defined in Table5 of this appendix.
    (amended 2009/05/11; no previous version)

Table 5 — Flammability Exposure Limit
(amended 2009/05/11; no previous version)

Minimum number of flights in MonteCarlo analysis Maximum acceptable MonteCarlo average fuel tank flammability exposure (percent) to meet 3percent requirements Maximum acceptable MonteCarlo average fuel tank flammability exposure (percent) to meet 7percent requirements
10,000
100,000
1,000,000
2.91
2.98
3.00
6.79
6.96
7.00
Date modified: