The conditions under which aircraft are compared do not necessarily reflect the conditions under which they may be operated. Indeed, it is rarely the case that the interior configuration used in an evaluation reflects the layout of a delivered aircraft. This is mostly because it is just not possible to assess with any precision how the aircraft will be assigned onto a network, which may itself evolve between the evaluation phase and the final delivery. 

During the early phases it is sensible to use a degree of conservatism into the evaluation. It does not make sense to be overly optimistic in the early stages of the evaluation as this can only serve to deliver unpleasant surprises later in the process. However, the assumptions should not be too conservative either, as penalties on payload, weight and fuel burn will only serve to give the impression that the aircraft is inadequate. 

Where an aircraft being considered is a totally new design, it is prudent to add more conservatism to some of the study parameters. However, generally it is wise to apply the same conditions for all aircraft under consideration avoid introducing bias. 

The manufacturers will push for assumptions that enable aircraft to be marketed in the best light and will be reluctant to accept parameters that unduly penalize the performance or economics of the aircraft. the manufacturer should be allowed sufficient flexibility to introduce elements of value that might otherwise remain hidden.

When compiling the evaluation it should be understood that the content may be applied not only to new-build aircraft currently under production, but to used aircraft that are already in service, and aircraft still in the project stage for which the level of data will be reduced. The degree of conservatism applied will be different in each case. 

The evaluation must provide information concerning the numbers of desired guests and staff seating. toilets, galleys, storage, and arrangements for sleeping and rest areas. The derivation of the Layout Of Passenger Accommodation, or ‘LOPA’, is a vitally important exercise as the configuration drives the weight of the aircraft, the performance, payload capability and economics. Should adjustments be made at a later stage the knock-on effects could be significant. 

Details the operational items and passenger weights (including baggage allowances), preferences for carrying passenger baggage and cargo, plus cargo and fuel densities. 

OPERATIONAL ITEMS WEIGHTS.
Operational items refer to the equipment and supplies necessary for the flight operation but do not include passengers, baggage, or cargo. This can include:
CREW - Varies by the number and roles but typically assumes standard weights unless actual weights are provided.
‍CDepends on the flight duration and service level. Weight can vary significantly.
‍EStandard weights as per the equipment type and regulatory requirements.
‍OIncludes items like magazines, blankets, etc., which are usually accounted for with standard weights.

PASSENGER WEIGHTS.
Passenger weight calculations often use standard average weights per passenger. These weights can vary by season (winter clothing is heavier) and region. The weights include:
‍AStandard weights are provided by aviation authorities.
CHILDREN & INFANTS - Usually have lower standard weights.
BAGGAGE ALLOWANCE - Could typically range from 15 to 30 kg (33 to 66 lbs) per passenger. Baggage weight is critical for calculating the total weight and balance of the aircraft.

PREFERENCES FOR CARRYING BAGGAGE & CARGO
Customers have specific policies and preferences for carrying passenger baggage and cargo, focusing on safety, efficiency, and customer satisfaction. This includes:
PRIORITIZING ESSENTIAL ITEMS - Items necessary for passenger comfort and safety.
MAXIMIZING UTILIZATION - Efficiently using available cargo and baggage space to optimize fuel consumption and range.
SPECIAL HANDLING ITMES - Prioritizing the loading and unloading of fragile, perishable, or high-value items.

CARGO & FUEL DENSITIES
CARGO DENSITY - Varies significantly based on the type of cargo. For example, dense cargo like machinery has a higher weight-to-volume ratio compared to lighter cargo like textiles. Knowing cargo density helps in optimizing space and weight distribution.
FUEL DENSITY - Aviation fuel (Jet A1) has a density of approximately 0.8 kg/L (6.7 lbs/gal) at 15°C (59°F). The density can vary slightly with temperature, which is crucial for calculating the total fuel weight.

FUEL CONSIDERATIONS
FUEL LOAD - Determined by the flight plan, considering distance, alternate airports, reserves, and contingencies.
FUEL PLANNING - Essential for ensuring that the aircraft carries enough fuel for the journey, plus reserves, without exceeding maximum takeoff weight limits.

The customer has to be assured that the aircraft can be handled at all of the airfields in the current and future network. The manufacturer must supply aircraft dimensions, pavement loading limits, ground maneuvering requirements, ground support equipment that is specific to the aircraft type and data concerning the weight and balance of the aircraft. Most of these data can be found in the Airport Planning Manual for the aircraft.

This is an opportunity for the client to indicate any specific requirements in how the economic and financial analysis should be conducted. For example, the customer may wish to see numbers relating to an average block time or average utilization.

The Aircraft Selection Criteria and the Aircraft Evaluation documents, form the core of the Request For Information (RFI) that can be sent to the selected aircraft manufacturer. It is typical to give the manufacturers a target date for submission of their responses. However, as the RFI is not a formal document and the manufacturers are under no obligation to respond by a set date, sufficient time should be allowed, placing undue pressure on the manufacturers at this stage is counter-productive as generating a thorough and accurate set of data involves numerous specialists. 

As the manufacturers are invited to present their results, they will augment their responses with marketing messages to support their products. Manufacturers should be encouraged at this stage to offer additional ideas and concepts, especially as they will have access and analytical tools that are designed specifically for fleet planning purposes.

It would be unusual if manufacturers responded perfectly to the RFI at the first attempt. Compliance is not a contractual matter, so deviations may be accepted providing efforts are made to correct any changes to the assumptions to all manufacturers equally. Keeping track of such changes is important to maintain a level playing field. 

A usual consequence of the first round of results is that the manufacturers would be asked to refine their RFI responses. Once a satisfactory set of data has been provided from all the manufacturers the client can elect eliminate the unsuitable aircraft. 

This is often the largest section in the evaluation Here, would typically contain instructions for the calculation of the take-off, temperature conditions to be applied, and specific dimensions of airfields to be considered in the analysis, including their ambient conditions. For route performance would contain information concerning the flight profile, a list of routes to be analysed along with distances to be used and the wind conditions to be applied.