AC 120-38
ADVISORY CIRCULAR -- DEPARTMENT OF TRANSPORTATION Federal Aviation Administration Washington, D.C.
FAR GUIDANCE JWTERIAL Subject: TRANSPORT CATECORY AIRPLANES CABIN OZONE coNCENTRATIONS 1 PURPOSE. This advisory circular provides guidance concerning acceptable means, hut not the only means, for an air carrier to demonstrate cw>mpliance with the maximum permissible cabin ozone (03) concentrations established by Section
121.578 of the Federal Aviation Regulations (FAR).
2 REIXTED FAR SECTIONS.
2i.832.
This advisory circular is also related to Section 3 RELATED READING MATERIAL. Additional information on ozone concentrations may be found in the following documents:
a. Federal Aviation Administration (FAA) documents:
(1) Simultaneous Cabin and Ambknt Ozone Measurements on Two Boeing 747 Airplanes, Volume I - Report Number FAA-EE-79-05 (NTIS Accession Number ADA 079 114).
(2) Guidelines For Flight Planning During Periods of High Ozone Occurrence - Reprt Number FAA-E(_)-78003 (NTIS Accession Number ADA 050 988).
(3) Effects of Ozone on Exercising and Sedentary Adult Men and Women Representative of the Flight Attendant Population (NTIS Accession Number ADA 080 045).
- Report Number FAA-A?!-79-20
(4) Ozone Concentration By Latitude, Altitude, and Month, Near 80' k7est - Report Number FAA-AEQ-77-13 (NTIS Accession Number ADA 046 956).
Copies of these reports my be purchased from the National Technical Information Service; Springfield, Virginia 22161.
b Federal Aviation Administration Advisory Circular 00-52, Ozone Irritation During High Altitude Flight. Copies of this advisory circular may be obtained free of charge-from the U.S. Department of Transportation; Publications Section M-443.1, Washington, D.C. 20590.
Initiated by: flK260
AC m-38
c. National Aeronautics and Space Administration Documents:
lo/lo/80
(1) Ozone Contamination in Aircraft Cabins - Report Number NASA CP-2066 (NTIS Accession Number N 79-21021).
(2) Procedures for Estimating the, Frequency of Corrmercial Airline Flights Encountering High Cabin Ozone Fields - Report Number NASA Tp-1560 (NTIS Accession Number N 79-33171).
Copies of these reports may be obtained from the National Technical Information Service; Springfield, Virginia 22161.
d National Primary and Secondary Ambient Air Quality Standards, Title 40, Chap&r 1, Subchapter C, Part 50 - Environmental Protection Agency final rulemaking, Federal Register, Volme 44 I Number 28, Page 8202 - Thursday, February 8, 1979.
4 0 BACKGROUND.
a. Natural ozone is formed primarily above the tropopause in the upper atmosphere as a result of the action of ultraviolet light on oxygen molecules. The amount and distribution of natural ozone in the atmosphere varies with latitude, altitude, season, and weather conditions. [See paragraph 3a(2).] ?Ihe highest concentrations in the northern hemisphere are generally found at high altitude over high latitude locations during the winter and spring.
b In late 1976, complaints were received from crewmars on high altitude, high latitude, long range flights which described discomforts such as eye irritations, coughing, nose irritations and chest pains. Subsequent research determined that some of these symptoms could be attributed to ozone in the aircraft cabin. Significant ozone ancentrations were occasionally measured in the cabin of aircraft on high latitude, high altitude flights and research studies cx>nducted in an altitude chamber demonstrated that significant ozone concentrations may produce similar symptoms in some persons.
c. Part 121 of the FAR has been amended so that a certificate holder may not operate a transport category airplane above flight level 180 unless it has successfully demonstrated to the Administrator that the concentration of ozone inside the cabin will not exceed .25 parts per million by volume, sea level equivalent, at any time; and time-weighted value of .l part per million by volume, sea level equivalent, for scheduled flight segments of more than 4 hours.
Compliance with these requirements should be shown by analysis and/or tests based either on airplane operational procedures and performance limitations or the certificate holder's operations. The analysis or tests must show either (1) that atmospheric ozone statistics indicate, with a statistical anfidence of at least 84 percent, that at the altitudes and locations at which the airplane will be operated that the permissible levels of cabin ozone ancentrations will not be exceeded; or (2) that the airplane ventilation systems, including any ozone control equipment, will maintain the cabin ozone concentrations at or below the permissible levels. Acceptable mans of conducting the required analysis or tests are discussed in paragraph 5 of this advisory circular.
2 p= 3
lo/lo/80 AC 120-38 d It is expected that research into the physiological effects of ozone and effeck methds for its control will continue to provide a greater understanding of its effects on persons and will increasingly provide mre effective methods to eliminate excessive ozone quantities. Nevertheless, current technology is adequate to eliminate excessive levels of ozone in aircraft cabins. Filters and catalytic converters for reducing cabin ozone-concentrations are available which can be installed on affected aircraft types. However, several additional methods exist which may, in certain cases, maintain cabin ozone ooncentrations at or below the maximum permissible levels. An air carrier may use any of the methods contained in this advisory circular if the analysis or tests oonducted show that the method(s) chosen are effective.
e. Since each of the various methods has certain beneficial aspects, one method is not favored over any other. However, the FAA intends to anduct inflight spot checks to ensure oompliance with the standards.
5 . MEANSOFCWIPLIANCE.
a. Acceptable means of demonstrating compliance includes any one or a combination of the following:
(1) A statistical analysis which is based on acceptable atmospheric ozone statistics, the types of aircraft flown, and the route structure used in the air carrier's operation.
(2) A statistical analysis which is based on actual measurements of cabin ozone concentrations for the types of aircraft operated and obtained over routes or areas representative of the air carrier's route structure.
(3) Modifications to the aircraft by an air carrier, under a Supplemental Type Certificate (SIC), FAA Fbrm 337 approval, or an engineering order/authorization to comply with a manufacturers approved service bulletin, which reduces the ozone concentrations to acceptable levels in the aircraft cabins.
(4) Modifications to the aircraft by the manufacturer or design changes which reduce cabin ozone levels to acceptable levels.
(5) Modifications to operational procedures, such as the use of a higher stage bleed air or the use of recirculation antrols, to reduce ozone to acceptable levels.
(6) Flight planning procedures to adjust the flight altitude and/or route of flight to reduce cabin ozone to acceptable levels.
b Examples of the specific means or ambination of means which may be used by an air carrier to demonstrate mpliance are discussed in detail in paragraphs 6, 7, and 8 of this advisory circular.
AC 120-38 6 . STATISTICAL ANALYSIS.
a. If the carrier elects to use statistical analysis to demonstrate compliance, the method used should demonstrate with a statistical confidence level of 84 percent that the cabin ozone levels will be within acceptable limits.
b The ozone data base used in the analysis should include sufficient data to demonstrate qliance within the area of operation on a month-tomonth basis. Any statistical analysis should be based on acceptable atmospheric ozone statistics, actual inflight measurements, or a oomhination of both.
c. Acceptable atmospheric ozone statistics are contained in the publications listed in paragraph 3a(2) and 3a(4). If actual inflight measurements are used, they should provide a sufficient data base to establish the required statistical confidence level and contain monthly altitude, latitude and longitude resolution elements equivalent to those in Appendix A of the publication listed in paragraph 3a(2) for the type(s) of airplanes flown and the operations anducted. Additionally, actual inflight cabin ozone measurements should be obtained with equipment which has been periodically calibrated and maintained in accordance with approved Environmental Protection Agency (EPA) procedures.
d One of the elements which should be considered in a statistical analysis based'on acceptable ambient ozone statistics is the ozone dissociation (destruction) rate for the environmental control system installed in a particular type of airplane. This factor determines the percentage of the ambient ozone which is ultimately introduced into the cabin environment. The ozone dissociation rate is applied to the ambient ozone statistics to determine the cabin ozone statistics for that flight altitude, time and location.
e. Normally, the dissociation rate has been determined by simultaneous inflight measurements of ambient and cabin ozone levels. However, other methods, such as laboratory measurements or an engineering analysis, may be used to establish the dissociation rate for a particular environmental control system if these methods are shovm to be accurate and reliable.
f still'be In cases where the dissociation rate is unknown, a statistical analysis may used to show compliance. In this case, it may be necessary to assume that the rate is zero and the cabin levels are equal to the ambient levels.
g Statistical analysis required by this advisory circular may be obtained from pools'of data formed by cooperation between operators and manufacturers. Data to determine the cabin ambient ozone dissociation (destruction) rate for the statistical analysis approach of Appndix 1 of this advisory circular IMY be accepted if it comes from other operators of the same type of aircraft with the same cabin air handlinq systemSI or is otherwise shown to be appropriate. Cabin ozone data from - these aircraft may also be accepted for demonstrating compliance with the permissible ozone level if the data are taken in the same geographic area.
h Acceptable means of conducting this statistical analysis are contained in Appendix 1 of this advisory circular and the publication listed in paragraph 3c(2).
However, either of these methods should use acceptable ozone statistics (see Appendix 2).
4 Par 6
lo/lo/80 AC 120-38
a. Design changes/modifications my be used to demnstrate compliance if analysis and/or tests show that these mthods reduce the cabin ozone concentrations to acceptable levels for each type of aircraft flown and each operation conducted.
The tests, if required, nay be conducted in a laboratory, inflight, or a -ination of both. A statistical analysis Wed on acceptable ozone statistics my also be used to demonstrate that the ozone dissociation rate for the device(s) installed will reduce the cabin ozone to acceptable levels.
b Once the ozone dissociation rate has been established for a particular devi&. the potential mximm cabin ozone concentration and the time-weighted averages, if apy?mpriate, are determined by applying the dissociation rate tc> the ambient ozone concentrations contained in the statistical analysis. The disse ciation rate should be high enough to demonstrate compliance on a mnth-by-month basis within the area of operation.
c. In any case, the air carrier should demonstrate to the Administrator that the design changes/modifications and/or the equiment installed will reduce the cabin ozone concentrations to acceptable levels in each type of aircraft used and for each mute flown by its aircraft. The ozone dissociation equipment, if installed, should be included in the air carrier's approved maintenance program and should be inspected, repaired and/or replaced in accordance with approved procedures. The initial service life of the ozone dissociation equipment should be established through analysis and tests.
d Examples of a procedure for demonstrating compliance after installation of equ&ent with a tim ozone dissociation rate are contained in Appendix 1 of this advisory circular.
8 0 OPERATIONAL AND/OR FLIGHT PLMNING PRKEDURES.
a. If an air carrier chooses to adopt operational or flight planning procedures to demonstrate compliancer these procedures should be shown to reduce cabin ozone concentrations to acceptable levels for each type of aircraft sed and for each route or area flown by these aircraft.
b The required analysis and/or tests should use inflight measurements and/or statiitical data from acceptable ozone statistics to show that the operational and/or fliyht planning procedure to be sed will reduce the cabin ozone concentrations to acceptable levels. The ozone dissociation (destruction) rate for the environmental antrol system installed in the particular type(s) of airplanes used by the air carrier should be considered when conducting a statistical analysis.
This factor determines the percentage of the ambient ozone tiich is ultimately introduced into the cabin environment. If the dissociation rate is unknown, it may be neccesary to assume that the rate is zero and the cabin levels are equal to the ambient levels. ,
c. In one method, the location of high ozone concentrations muld be prtiicted . and flight planning procedures would route the flight to reduce the cabin ozone to acceptable levels. Similar methods Roy be used to determine when operational procedures, such as using high stage bleed air, or sing recirculation controls, are Par 7 5
AC 120- 38 lo/lo/80 necessary to dissociate sufficient .ozone to obtain compliance. However, data from inflight measurements are necessary to demonstrate that these procedures are effective. This is due to the difficulty of reliably predicting ozone cx>ncentrations at normal flight altitudes. Furthermore, these data should show that the techniques used to predict ozone concentration levels for a particular flight indicate that there is a statistical confidence level of 84 percent that the flight will not exceed the permissible maximum concentrations at any pint along the route of flight.
d An alternate method would be to restrict the flight altitude on certain flights or segments of flights to achieve cwnpliance. Acceptable ozone statistics should be used to oonduct an analysis which shows that the flight altitude(s) authorized fora particular route or area of operation will maintain the cabin ozone concentration within acceptable limits. In me cases, these restrictions may be necessary only during certain months. An example of such a statistical analysis to demonstrate mmpliance is oontained in Appendix 1 of this advisory circular.
e. In any case, sufficient data should be provided to show the Administrator that these procedures are reliable and effective in reducing cabin ozone to acceptable levels for each type of aircraft and each route or area flown by these aircraft.
9 0 OPERATIONAL APPm@JL.
a. The application for approval of the method(s) proposed by the air carrier to reduce cabin ozone to acceptable levels should be submitted to the FAA certificate holding office for review and approval at least 30 days prior to using the propsed method(s) in air carrier service. This application should contain any pertinent airworthiness approvals, as well as the necessary supporting data, and the proposed amendments to the operations specifications.
b The supporting data should show that the method(s) to be used by the air carrier will' reduce cabin ozone ancentrations to acceptable levels for each type of aircraft used and each route or area flown by those aircraft. The operations specifications should reflect any operational restrictions necessary-to achieve a . compliance.
c. If the air carrier demonstrates that the method(s) to be used are effective, approval should be granted by amendment to the operations specifications. Approval in the operations specifications may be granted by area of operation, by individual routes, or a combination of both. The approval should include the restrictions
(i.e., maximum flight altitude, operational procedures, aircraft difications) necessary to achieve compliance. The restrictions should be applicable to the types of aircraft operated or types of operations conducted, or both.
10 0 REQUESTS FOR DEVIATION FROPl THE COUPLIANCE PEPJOD.
a. The FAA has determined that the 12lnonth period provided for air carriers to . comply with this rule is reasonable and adeqwte. However, the new Section 121.578 allows a certificate holder to obtain an authorization to deviate from these requirements by an amendment to its operations specifications, if it shows that due to circumstances beyond its control or to unreasonable economic burden it cannot comply for a specific period of time, and submits a plan acceptable to the 6 Par 8
Administrator to effect compliance to the extent possible. A deviation can be authorized in circumstances such as equipment delivery delays or short-term use of aircraft, when the certificate holder shows that, through flight planning or other means, it attempts to avoid areas of cabin ozone concentrations above the limits given in the rule. *- b Any request for deviation should state the reasons why compliance -MC& be demon&ted during the time period and II&Y these factors are beyond the control *of the air carrier. The request should also contain a compliance schedule and a plan to effect compliance to the extent possible which are acceptable to the Administrator.
c. The request for deviation should be submitted to the FAA certificate-holding office at least 60 days before the compliance date of February 20, 1981, stated in Section 121.578 of the FAR.
KENNETH S. HUNT Director of Flight Operations Par 10 7
lo/lo/80 AC 120-38 Appendix 1 APPENDIX lo EXAMPLES OF STATISTICAL F;NALYSIS 1 0 PURPOSE. This appendix contains illustrations of a method using statistical analysis to demonstrate compliance with maximum and time-weighted average permissible cabin ozone concentrations established by Section 121.578 of the Federal Aviation Regulations (FAR). -- 2 l EXPLhNATION OFTERMSANDSYME3OLSo
a. OZMAX is the permissible maximun ozone omcentration inside an airplane cabin as established by FAR Part 121 which may rW exceed a value of 0.25 parts per millionby volume (ppnv), sea level equivalent (SE), at any point in time.
b OZWA is the permissible time-weighted average (TWA) of the ozone concekration inside an airplane cabin over a flight segment as established by FAR Part 121 which may rw>t exceed a value of 0.1 ppnv, SLE, for each flight segment that exceeds 4 hours.
c. OZSIE is ozone concentration in ppnv referenced to standard conditions of 25' C and 760 millimeters of mercury pressure.
d (P/p,) is the ratio of cabin pressure (P) to sea level pressure PO).
This ratio is used to obtain the SLE ozone concentration from the ozone omcentration at altitude assuming the cabin temperature is 25O C. OZSLE = (P/Po)(O$.
Some representative values which can be used in operational calculations are:
For P of: P/P&s:
5000 feet 0.83 6000 feet 0.80 7000 feet 0.77 8000 feet 0.74 NOTE: The use of standard P/P, tables can result in errors of up to 7 percent dueto the use of temperatures other than 25O C.
e. R is the retention ratio of the ambient (outside) ozone which enters the airplane cabin after going through the air mnditioning system and, in mst cases, the engines. Normally, the retention ratio is from 0.75 to 1.00 without cabin air recirculation and can be as low as 0.4 to 0.6 with cabin air recirculation.
However, the retention ratio for a particular aircraft may differ from these values depending on the cabin air exchange rate, the interior surface to volume relationship, and the amount of cabin air recirculated.
f E is the efficiency of a filter or catalytic oonverter installed to remove portion of the ambient ozone before it enters the airplane cabin. For the purpose of this appendix, the mrd "filter" is used to describe either type of device. An airplane without a filter muld have E = 0.
a g 0 T18 is the flight time above 18,000 feet.
.
AC 1200 38 Appendix 1 10/10/80 h 0 TFS is the total flight segment time (block time). .
i. 0216 is the estimated ambient ozone mncentration obtained from statistics with a confidence level of 84 percent. As explained iv Appendix 2 of this advisory circular, preferable data for this purpose are the ozonesonde statistics given in Appendix A of Report FAA-E&78-03. Examples of these data for February are reproduced on pages 12 to 19 of this appendix. In using these data, it should be remembered that they are central values for five degrees latitude and 2000 feet altitude boxes.
.
I Although there are many flight routes which are not specifically oovered by the dka on these pages, the data can be used to interpolate the ozone statistics for any flight route. An example of this is shown in Figure 1 for the month of February where 0216 values are presented for flight levels 410, 390, and 370, The heavy dashed areas are the regions covered by the ozonesonde data. The Japan and western Europe data used in this example have been linearly interpolated to obtain resolution increments of five degrees similar to those used in the eastern and western North American regions. (For 3ON, the Japan ozone data have been set to one-half the value at 32N since a linear interpolation gives negative values).
17here data exist at a c&non latitude, they have been linearly interpolated to determine the values for the Pacific and Atlantic areas and are shown in the lighter dashed regions. For latitudes where there are no Japan or western Europe data, the appropriate North American data should be used. The following examples of this procedure to determine 0216 values for flight level 410 are given:
Longitude Latitude 0216 Obtained From Extension of the 160 E 160 E 40 w 40 w 65 N 70 N 65 N 70 N
1.2ppv western North American data
1.3pFll-w eastern North American data Llppnv eastern North American data 103ppnv eastern North American data For the southern hemisphere, the data can be (1) obtained from a mirror image of the northern hemisphere data with a 6-month seasonal shift. For example, ozone data for Janaury at 45 S, 80 W ~~)uld be obtained from the July ozone data at 45 N, 80 k7; or
(2) calculated by averaging the northern hemisphere data over all longitudes at a given north latitude and using the resulting value for the same south latitude, again with a 6-month seasonal shift.
3 l DISCI1JSSIOK In this appendix, the ozone statistics are used in 3 types of examples.
a. ?pel - Direct determination if a flight a;>mplies with either the maximum or 1F7A cabin ozone concentrations established by FAR Part 121.
b. qpe2 - Determination of the filter efficiency (E) required for a particular flight to comply with the cabin ozone ancentrations established by FAR Part 121.
lO/lO/BO AC 120-38 Appendix 1
c. Type 3 -Determinat ion of the maximum flight altitude an airplane cx>uld fly given a geographical region, latitude and time of year and still amply with the cabin ozone concentrations established by FAR Part 121.
4 EXAMPLES - MAXIMUM CABIN OZONE CONCENTRATION (0.25 ppnv, SLE). The maximum cabin concentration using ozone statistics should be determined at each point along the route of flight and is given by:
OZMAX = (l-E)(OZ16)(R)(P/Po) (Equation 1) In all examples, the value for R is 0.8 and the value for (P/P,) is 0.77 (a cabin altitude of 7,000 feet). Equation 1 then beames:
OZMAX = (0.8)(0.77)(1-E)(OZl6) = (0.62)(1-E)(OZ16) (Equation 2)
a. Type 1 -Examplet o determine if any point along a flight route is in compliance with the maximum cabin ozone concentration (0.25 ppnv, SLE). From the ozonesonde statistics on Page 16 of this appendix (Page A-15 of the ozonesonde statistics) look up 0216 using the following example information:
Region: eastern North &nerica Month: February Fliaht level: 370 (1 Page 16 of
0.50 pp"v.
Therefore Case 1, Mtitude: 50' North this appendix (Page A-, 15 of the ozonesonde statistics) gives 0216 = assuming E = 0, or no filter):
OmAx = (0.62)(0.50) = 0.31 ppnv THIS POINT ALlXVG 'IVE FLIGHT R0UTE KKJLD NOT HAVE DEMONSTRATED COMPLIANCE WITH THE WXIMUTI CABIN OZONE CONCENTRATION ESTABLISHED BY FAR PART 121.
(2) Case 2. Latitude: 40' North Page 17 of this appendix (Page A-16 of the ozonesonde statistics) gives 0216 =
0.40 ppw.
Therefore (assuming E = 0, or no filter):
0mAx = (0.62)(0.40) = 0.25 ppnv.
THIS POINT ALI3NG THE FLIGHT WUTEZ WZULD HAVE DEMONSTRATED CWPLIANCE WITH THE MAXIMUM OZONE CONCENTRATION ESTABLISHED BY FAR PART 121.
AC 120- 38 Appendix 1 10/10/80
b. Type20 Example to determine the filter efficiency required to show cor~@iance at a pint along the flight route with the maximum cabin ozone concentration. Equation 2 can be rewritten to determine E, the filter efficiency:
-- . (Equation 3) For OZMAX = 0.25 pmv, Equation 3 becomes:
(Equation 4)
(1) Case 1. Latitude:
0216 50° North
0.50 ppv = 1 - (0.80) = 0.20 = 20% INSTALLATION OF A FILTER WHICH REMOVED 20 PERCEX? OF THE OZONE Eil!mmxTHEcABIN WOULD ENABLE THIS POINT WNG THE FLIGHT IDUTE ?o SHOW CT)MPLIANCE WITH THE MAXIMUM CABIN OZQJE CONCEZNTRATION ESTABLISHED BY FAR PAKI' 121.
(2) Case 2. Latitude: 45O North NO FILTER REQUIRED FOR THIS POINI AlxlNG TUE FLIGHT FDUTE AS COMPLIANCE WITH THE MAXIMUM CABIN OZONE CONCENTRATION ITM3LISHED BY FAR Pm 121 WAS SHMN DURING EXMJPLE TYPE 1, CASE 2.
(3) Variation of Type 2. The filter efficiency required for an airplane to show compliance with the mximum cabin ozone concentration for a point along any flight route can be determined using the method of the Type 2 exam@e. mr a mrst case analysis, the following assumptions are made:
P/P, = 0.74 (Cabin Altitude of 8,000 feet- maximum pressure differential of
8.9 pounds per square inch at 45,000 feet) R= 1.0 (Al.1 ambient ozone enters the airplane cabin) At flight level 450 the mximm ozone concentration at an 84 percent confidence level the ozone statistics baragraph 3(a)2, Appendix A] is found to be I.8 ppmv during February at 80° nortfl latitude in the eastern North Anerican region. This is shown on page 15 of this appendix.
Equation 1 can be written as:
E=l- WJA?C [ (OZ16) (RI <p/p,) 1 4