# Requirement 4: Missed Approach Climb

## Background

The climb gradient for missed approach is determined from the aviation regulations:

JAR 25.121 Climb: One-engine-inoperative.
(d) Discontinued Approach. In a configuration in which VS does not exceed 110% of the VS for the related all-engines-operating landing configuration, the steady gradient may not be less than
2·1 % for two-engined aeroplanes,
2·4 % for three-engined aeroplanes, and
2·7 % for four- engined aeroplanes, with -
(1) The critical engine inoperative, the remaining engines at the available take-off power or thrust;
(2) The maximum landing weight; and
(3) A climb speed established in connection with normal landing procedures, but not exceeding 1·5 VS.
(4) Landing gear retracted.*

* Number (4) of § 25.121 (d) exists only in JAR 25 but not in FAR Part 25.

## Equation

The missed approach is similar to the second segment situation where one engine of the aircraft is inoperative. The thrust of the remaining engine(s) has to be enough to climb again as required. The second segment climb equation is expanded by the mass ratio determined already in the landing field calculation:

The climb gradient can simplified similar to the second segment:

## Data

### Lift to Drag Ratio

The lift to drag ratio is calculated from the following equation:

The lift coefficient is the landing lift coefficient divided by 1.69, because the climb speed is 1.3 times the stall speed.
The drag coefficient consists of five parts:

where the
• Oswald's airplane efficiency factor e is 0.7,
• wing aspect ratio A is given or taken from statistics,
• drag coefficient at zero lift cD, 0 is assumed to be 0.02,
• landing gear drag coefficient cD, gear is 0.015,
• slat drag coefficient cD, slat is neglected and set to zero,
• flap drag coefficient cD, flap:
for cL = 1.3 : flap deflection 15° => cD, flap = 0.01
for cL = 1.5 : flap deflection 25° => cD, flap = 0.02
for cL = 1.7 : flap deflection 35° => cD, flap = 0.03 .

 background of mass relation   statistics of aspect ratio   next: calculation of takeoff thrust to weight

## Calculation

With given values of takeoff lift-coefficient, wing aspect ratio, mass ratio and the number of engines it is now possible to calculate the ratio between takeoff trust and takeoff weight. The landing gear is retracted according to JAR 25 and extended in the FAR 25.

In the table are typical start values already entered. The graph is presented in Figure 2.
maximum landing lift coefficient
cL,max,L [ - ]
landing gear:
retracted (JAR 25)
extended (FAR 25)
number of
engines (N) :
2
3
4
landing to takeoff mass (range):
0.91 (short)
0.82 (middle)
0.73 (long)
custom:
wing aspect ratio
A [ - ]
result :
 takeoff thrust takeoff weight [ - ]

Figure 2: chart for calculated results

The takeoff thrust to weight ratio of the aircraft must be above the pink line to fulfil the requirement for the missed approach condition. (Bear in mind: Thrust means climb rate.)

## Results compared

Takeoff thrust to weight ratio of selected aircraft JANE'S 1995-98
 Aircraft Takeoff thrustTakeoff weight   [ - ] Airbus A 300-600B Airbus A 310-300 Airbus A 340-300 Antonov AN 124 Boeing B 737-600 Boeing B 777 McDonnell Douglas MD11 Tupolev TU 204 0.308 - 0.324 0.290 - 0.356 0.220 - 0.240 0.231 0.307 0.292 - 0.304 0.299 - 0.309 0.341 - 0.413

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