5. IN-FLIGHT REQUIREMENTS 

5.1. In-Flight Failure 

“JAR-OPS 1.400 Before commencing an approach to land, the commander must satisfy himself that, according to the information available to him, the weather at the aerodrome and the condition of the runway intended to be used should not prevent a safe approach, landing or missed approach, having regard to the performance information contained in the Operations Manual. The in-flight determination of the landing distance should be based on the latest available report, preferably not more than 30 minutes before the expected landing time.” 

In the event of an aircraft system failure occurring in flight, and affecting landing performance, the runway length to be considered for landing is the actual landing distance without failure multiplied by the landing distance coefficient associated to the failure. 

These coefficients, as well as the ALDs for each runway state, are published in Airbus’ operational documentation (Flight Crew Operating Manual and Quick Reference Handbook). 

Note that the required landing distance concept no longer applies and the margins retained for alternate airport selection are at the captain’s discretion. 

5.2. Overweight Landing Requirements 

In exceptional conditions (in-flight turn-back or diversion), an immediate landing at a weight above the Maximum Landing weight is permitted, provided pilots follow the abnormal overweight procedure. 

The aircraft’s structural resistance is protected for a landing at the Maximum structural Takeoff Weight (MTOW), with a rate of descent of -360 feet per minute. 

Nevertheless, the minimum required air climb gradients, in the case of a go-around, must be complied with. For certain aircraft types, the go-around can be performed in CONF 1+F if the climb gradient cannot be achieved in CONF 2. The landing configuration is then CONF 3. That’s possible when VS1g (CONF 1+F) < 110% VS1g (CONF 3). 

5.3. Fuel Jettisoning Conditions 

“JAR/FAR 25.1001 A fuel jettisoning system must be installed on each aeroplane unless it is shown that the aeroplane meets the climb requirements of Approach Climb gradient and Landing Climb gradient at maximum take-off weight, less the actual or computed weight of fuel necessary for a 15-minute flight comprised of a take-off, go-around, and landing at the airport of departure with the aeroplane configuration, speed, power, and thrust the same as that used in meeting the applicable take-off, approach, and landing climb performance requirements of this JAR-25.” 

When the Maximum Takeoff Weight (MTOW), less the weight of fuel necessary for a 15-minute flight (including takeoff, approach, and landing at the departure airport) is more than the maximum go-around weight, a fuel jettisoning system must be available. 

 

F. CRUISE 

1. GENERAL 

1.1. Introduction 

The main objective of the previous chapters is to comply with the airworthiness requirements of JAR/FAR 25 and JAR-OPS 1/FAR 121. This section deals with another objective. That of decreasing Direct Operating Costs (DOC). 

Direct Operating Costs include: 

Fixed costs (taxes, insurance, etc…), 

Flight-time related costs (crew, hourly maintenance costs, depreciation), 

Fuel-consumption related costs. 

The right choice of flight level and speed allows these DOCs to be minimized. In other words, as time and fuel consumption are closely related, cruise planning is established by making the right speed and flight level choices. In the following chapters, we will review some speed and altitude optimization criteria. 

1.2. Specific Range 

The specific range (SR) is the distance covered per fuel unit. 

Basically speaking, the specific range is equal to: 

ground speed (GS)

SR (Ground) = 

fuel consumption per hour (FF) 

Considering air distance, the specific range is equal to: 

true air speed (TAS)

SR (Air) = 

fuel consumption per hour (FF) 

As TAS is expressed in nautical miles per hour (NM/h), and Fuel Flow (FF) in kilograms per hour (kg/h), the SR is expressed in NM/kg or NM/ton. 

Moreover, SR depends on aerodynamic characteristics (Mach and L/D), engine performance (Specific Fuel Consumption)1, aircraft weight (mg) and sound velocity at sea level (a0). 

1 The Specific Fuel Consumption (SFC) is equal to the fuel flow (FF) divided by the available thrust. It is expressed in kg/h.N (kilogram per hour per Newton) and represents the fuel consumption per thrust unit. 

2. SPEED OPTIMIZATION 

2.1. All Engine Operating Cruise Speeds