JammedStab
9th Sep 2016, 18:22
According to an article I am reading on performance margins,
"The requirement to factor the headwind by 50% and the tailwind by 150% in takeoff performance calculations is intended to provide a margin for the possible variation of wind speed and direction during the takeoff. The magnitude of the accelerate stop distance margin associated with factoring a 10 knot headwind or tailwind is illustrated on Figure 3 for the 737-800, 777-200, and 747-400 at their respective maximum takeoff weight and sea level/30°C conditions. Relative to the scheduled AFM distance, shown in parenthesis, the actual distance is reduced by 5 to 6%."
So take a look at a particular aircraft that departs from a particular runway three days in a row.
On day one, the aircraft is at exactly its max allowable weight for the runway when the 10 headwind is taken into account.
On day two all conditions are the same except that the aircraft is much lighter. But there is a 10 knot tailwind and once again, it turns out to be at its exact maximum weight.
On day three there is no wind but all other conditions are the same. The aircraft is at a weight that is between what it was on the first two days but it turns out once again(very fortunately for the airline) to be able to takeoff and once again by coincidence happens to be at its maximum limiting weight.
In terms of performance margin, would it be correct to day that on the calm wind day, the aircraft had the least margin? In other words, the greater the tailwind or headwind in a performance-limited(acceleration-stop) takeoff, the greater the safety margin.
"The requirement to factor the headwind by 50% and the tailwind by 150% in takeoff performance calculations is intended to provide a margin for the possible variation of wind speed and direction during the takeoff. The magnitude of the accelerate stop distance margin associated with factoring a 10 knot headwind or tailwind is illustrated on Figure 3 for the 737-800, 777-200, and 747-400 at their respective maximum takeoff weight and sea level/30°C conditions. Relative to the scheduled AFM distance, shown in parenthesis, the actual distance is reduced by 5 to 6%."
So take a look at a particular aircraft that departs from a particular runway three days in a row.
On day one, the aircraft is at exactly its max allowable weight for the runway when the 10 headwind is taken into account.
On day two all conditions are the same except that the aircraft is much lighter. But there is a 10 knot tailwind and once again, it turns out to be at its exact maximum weight.
On day three there is no wind but all other conditions are the same. The aircraft is at a weight that is between what it was on the first two days but it turns out once again(very fortunately for the airline) to be able to takeoff and once again by coincidence happens to be at its maximum limiting weight.
In terms of performance margin, would it be correct to day that on the calm wind day, the aircraft had the least margin? In other words, the greater the tailwind or headwind in a performance-limited(acceleration-stop) takeoff, the greater the safety margin.