Appendix 6 APPENDIX 6. SAMPLE CG ENVELOPE DEVELOPMENT Outlined below is an example of the development of a center of gravity (CG) envelope construction for a 19-seat commuter category aircraft. The sample system uses a CG diagram displayed in inches. Operators’ systems may use a variety of methods to display CG diagram, including an Index system detailed in Chapter 2, Section 2 and in Appendix 3.
Sample Development of Weight and Balance System for 19-Seat Aircraft
a. CG Envelope Construction. The certified CG envelope provided by the manufacturer must be examined for the following curtailments.
(1) Variations to Passenger Seating (Outlined in Chapter 2). In this example, the window-aisle-remaining method was used considering a passenger weight of 189 pounds and using 3 passenger zones, where zone 1 is defined as rows 1−3, zone 2 is defined as rows 4−6, and zone 3 is defined as rows 7−9. (189 lb/pax is used since the operator will be using a nocarry-on baggage program as detailed later on in this sample exercise). The resulting curtailment for use of 3 passenger zones is 36,600 inch-pounds forward and aft.
(2) Variations to Passenger Weight (Outlined in Appendix 4). Since the sample aircraft falls into the group of aircraft requiring full evaluation of small cabin aircraft rules, application of a curtailment due to variations to passenger weight is required.
(a) Use of Passenger Zone Concept for Curtailment. Considering three cabin zones with each zone containing three rows in a 2-abreast configuration, the required row factor (see Appendix 4, Table 4-1) is 2.41. The row factor is multiplied by the standard deviation and the difference between average male and average female weights is added to provide the additional weight consideration. In our example, the standard deviation is calculated from the National Health and Nutrition Examination Survey (NHANES) data as 47 pounds, and the difference between average all-male and average passenger weights is 10 pounds. The resulting additional weight for curtailment is 47 × 2.41 + 10 = 123 pounds. This additional weight is applied per the window-aisle-remaining concept for each cabin zone independently and the results are summed to determine the amount of curtailment. In this case, the curtailment is found to be 23,791 inch-pounds forward and aft.
(b) Use of Row Count for Curtailment. When using row count, the required row factor is 2.96. The row factor is multiplied by the standard deviation and the difference between average male and average female weights is added to provide the additional weight consideration. In our example, the standard deviation is calculated from the NHANES data as 47 pounds, and the difference between average all-male and average passenger weights is 10 pounds. The resulting additional weight for curtailment is 47 × 2.96 + 10 = 149 pounds. This additional weight is applied as if a 2-row passenger zone concept is used for passenger seating.
The resulting curtailment is determined to be 16,657 inch-pounds forward and aft.
Appendix 6
(3) Variations to Fuel Density. Since the loading of fuel does not significantly shift the CG for the aircraft, it is not necessary to correct for variations in fuel density (i.e., the correction is negligible).
(4) Fuel Movement in Flight. Fuel movement has been considered by the manufacturer in the development of the certified envelope, making an additional curtailment unnecessary.
(5) Fluids. The sample aircraft does not have a lavatory and there is no catering.
(6) Baggage and Freight. The sample aircraft provides a baggage web in the aft baggage compartment, splitting the compartment into forward and aft sections. In our example, we assume the operator is making full use of this web and the movement of baggage is restricted. No curtailment is necessary.
(7) In Flight Movement of Passengers and Crew. Since there are no flight attendants and no lavatories on the sample aircraft, it is reasonable to assume that the passengers will remain in their seats for the duration of the flight. Therefore, it is not necessary to curtail the limits for passenger and crew in-flight movement.
(8) Movement of Flaps and Landing Gear. In the case of the sample aircraft, the manufacturer has included consideration of flap and landing gear movement in the development of the certified envelope. No additional curtailment is necessary.
(9) Fuel consumption. The fuel vector for the sample aircraft provides a small aft movement that requires a -8,900 inch-pounds curtailment to the aft zero fuel weight limits to ensure the aircraft does not exceed the aft limit as fuel is burned. This equates to a -0.8 inch curtailment at an estimated operational empty weight of 11,000 pounds with a linear transition to a -0.6 inch curtailment at MZFW of 16,155 pounds. In this example, the 8,900 inch-pounds is the fuel burn deviation that would bring the aircraft outside the aft CG limit during the course of flight.
b. Three operational curtailments to the sample aircraft CG envelope are required. These are for variations to passenger seating and passenger weight, and fuel burn-off. Figure 6-1 displays the operational CG envelope highlighting the required curtailments.
Appendix 6 FIGURE 6-1. OPERATIONAL CG ENVELOPE3 PASSENGER CABIN ZONES
19-Seat Aircraft Center of Gravity Diagram 9,000 10,000 11,000 12,000 13,000 14,000 15,000 16,000 17,000 18,000 272 276 280 284 288 292 296 300 304 Fuselage Station (Inches Aft of Datum) Weight (LBS) Max Ramp Weight Max Landing Weight Max Zero Fuel Weight Curtailment for Variations to Passenger Weight Curtailment for Fuel Burn Off Curtailment for Variations to Passenger Seating
Appendix 6
c. Assuming the operator wishes to widen the envelope, use of actual passenger seating (row count) may be used to eliminate the curtailment required for variations to passenger seating.
Figure 6-2 displays a CG envelope that makes use of actual passenger seating.
FIGURE 6-2. OPERATIONAL CG ENVELOPEACTUAL PASSENGER SEATING
19-Seat Aircraft Center of Gravity Diagram 9,000 10,000 11,000 12,000 13,000 14,000 15,000 16,000 17,000 18,000 272 276 280 284 288 292 296 300 304 Fuselage Station (Inches Aft of Datum) Weight (LBS) Max Ramp Weight Max Landing Weight Max Zero Fuel Weight Curtailment for Variations to Passenger Weight Curtailment for Fuel Burn Off
d. No-Carry-On Baggage Program. This example assumes a no-carry-on bag program.
This allows consideration of reduced passenger weight to 184 pounds (summer) and 189 pounds (winter). Carry-on bags checked at the gate or “plane-side loaded” will be counted as 20 pounds/bag. Bags checked at the ticket counter will remain at 30 pounds/bag.
Appendix 7 APPENDIX 7. CHECKLIST
Aircraft Type ___________________________ Region ________________________________ Route _________________________________ Aircraft Size / Carry-on Bag Assessment 1 Is the aircraft certificated under part 23 commuter category, part 25, or part 29 (or has equivalent performance data)?
(Yes or No) 2 What is the certified maximum number of seats for the aircraft?
If answer to (2) is greater than 70, then aircraft is large cabin size. If answer to (2) is less than 30, then aircraft is small cabin size. If answer to (2) is 30 to 70, then aircraft is medium cabin size. Continue with next question.
3a Does aircraft CG at OEW and at ZFW when fully loaded with passengers and cargo at 10 lbs/cu.ft. fall within the manufacturer's certified envelope limits? (Yes or No) 3b Does operator's loading schedule use passenger zone loading with no more than 4 rows per zone with not less than 4 zones or does operators loading schedule use passenger row count? (Yes or No) If answer to either (3a) or (3b) is yes, then aircraft weight & balance program may follow large aircraft cabin guideline. If answer to (3a) and (3b) is no, then aircraft weight & balance program should follow small cabin aircraft guidelines.
4 Does operator have in place a program that will prohibit placing of carry-on bag in passenger compartment?
(Yes or No) If answer to (4) is yes, then the aircraft is eligible to be included in a no carry-on bag program. If answer to (4) is no, aircraft is not eligible for carry-on bag program.
5 Aircraft weight & balance program guidelines (Small or Large) 6 Aircraft eligible for no carry-on bag program? (Yes or No) Passenger Weights Assumptions 7 Was a valid and current passenger weight survey performed? (Yes or No) The survey may include passenger weights and/or Male/Female ratios. If yes, then the passenger weights used should reflect the results of the survey.
8 Was a valid and current carry-on bag weight survey performed? (Yes or No) The survey may include checked bag weights and/or counts. If the answer to (8) is yes, then the passenger weights used should reflect survey results.
9 Will aircraft weight & balance program follow small aircraft guidelines? (Yes or No) If answer to (9) is yes, proceed with next question. If answer is no, go to question (12).
10 Will segmented passenger weights be used? (Yes or No) If answer to (10) is yes, use segmented passenger weights per Appendix 3 and go to question (12).
11 If answer to question (1) is Yes, will standard average passenger weights be used? (Yes or No) If answer to (11) is yes, use standard average passenger weights per Chapter 4.
12 If answer to question (6) is Yes, does operator intend to include aircraft in a no carry-on bag program? (Yes or No) If answer to (12) is yes, adjust passenger weight assumptions by -6 lb/pax.
Appendix 7
CHECKLIST (cont.)
13 Will actual, separate Male and Female weights be used? (Yes or No) If answer to (13) is yes, then individual male and female weights should be provided in (15) and (16).
If answer to (13) is no, then non-gender specific weights should be provided in (15) and (16).
14 Will Child weights be used? (Yes or No) If answer to (14) is yes, then child weights should be provided in (15) and (16).
Adult Male Summer Weight (lb) Adult Female Summer Weight (lb) Adult (non-gender specific) Summer Weight (lb) Child Summer Weight (lb) Adult Male Winter Weight (lb) Adult Female Winter Weight (lb) Adult (non-gender specific) Winter Weight (lb) Child Winter Weight (lb) Checked Bag Weight Assumptions 17 Was a valid and current checked bag weight survey performed? (Yes or No) If the answer to (17) is yes, then the checked bag weights used should reflect survey results. If no, then standard average checked bag weights as defined in Chapter 4 should be used.
18 If answer to question (6) is yes, does operator intend to include aircraft in a no-carry-on bag program?
(Yes or No) If answer to question (18) is yes, then carry-on bags checked plane-side should be counted as weighing 20 lb. each.
19 Does operator have an approved heavy bag program?
If the answer to (19) is yes, then bags over 50 lb and less than 100 lb are counted as 60 lb. If (19) is no, then actual weights should be used for bags weighing over 50 lb.
20 Domestic Checked Bag Weight (lb) 21 International Checked Bag Weight (lb) 22 Plane-side Checked Bag Weight (lb) 15 16
Appendix 7 CHECKLIST (cont.)
Center of Gravity Envelope Curtailment Which method of passenger seating assumptions will be used?
23 - Actual seat assignment? (Yes or No) If (23) is yes, then curtailment to the center of gravity envelope for variation in passenger seating not required. If yes, proceed to question (27). It may be appropriate for the operator to provide a small curtailment to accommodate passengers not sitting in their assigned seats if the operator does not have a program in place to ensure passengers are sitting in their assigned seats.
24 - Random seating with single cabin zone? (Yes or No) If (24) is yes, then curtailment to the center of gravity envelope for variation in passenger seating required per a documented method, such as Boeing window-aisle-remaining or Airbus root mean square methods. Passenger weight used in the loading system should be used when developing the curtailments. If yes, proceed to question
(27).
25 - Random seating with multiple cabin zones? (Yes or No) If (25) is yes, then curtailment to the center of gravity envelope for variation in passenger seating for each passenger cabin zone is required per a documented method, such as Boeing window-aisle-remaining or Airbus root mean square methods. The curtailments for each passenger cabin zone are summed to provide the total curtailment required for random passenger seating. Passenger weight used in the loading system should be used when developing the curtailments. If yes, proceed to question (27).
26 - Historically-based? (Yes or No) If (26) is yes, then forward and aft curtailments to center of gravity envelope should be calculated to a 95% confidence level based on recorded data. Passenger weight used in the loading system should be used when developing the curtailments.
27 Will aircraft weight & balance program follow small aircraft guidelines? (Yes or No) If answer to (27) is yes, operator should curtail center of gravity envelope for variations to passenger weight per Appendix 4.
28 Has aircraft manufacturer included variation to fuel density considerations in the development of the certified center of gravity envelope? (Yes or No) If the answer to (28) is no, then operator should curtail center of gravity envelope for expected variations in fuel density.
29 Does aircraft's fuel burn moment cause the aircraft to exceed the forward or aft center of gravity limits anytime during flight? (Yes or No) If answer to (29) is yes, then operator should curtail center of gravity envelope to ensure fuel burn will not result in a limit exceedance unless the manufacturer has already considered this in the development of the certified center of gravity envelope.
30 Has aircraft manufacturer included consideration of fuel movement in the development of the certified center of gravity envelope, e.g., fuel transfer between tanks? (Yes or No) If the answer to (30) is no, then operator should curtail center of gravity envelope for other fuel movement expected in flight.
31 Does aircraft have galley and/or lavoratory in the cabin? (Yes or No) If answer to (31) is yes, then operator should curtail center of gravity envelope for movement of potable water and/or lavoratory fluids in flight. Operator should also curtail for movement of passengers and crew members to lavoratories and flight attendant with serving cart moving through cabin.
32 Does the operator use procedures which ensure that the cargo is loaded uniformly throughout each compartment? (Yes or No) If answer to (32) is no, then operator should curtail center of gravity envelope to accommodate expected shifting of cargo load.