A Brief Analysis of Takeoff Safety Concerning the Proper Decision Making of GO/NO GO
By Ehsan Mirzaee
Introduction: Do more planes crash on takeoffs or landings? This is a challenging question for some people and an easy, clear one for others. According to official statistics, landing phase of a flight is the most dangerous phase, noticing the number of incidents and accidents occurred during this phase. In this final phase of flight, pilots are required to take into consideration more variables in a shorter period of time. They should deal with speed, altitude, pitch corrections, comply with ATC instructions, and at the same, time monitor all other systems and instruments to know if they are working properly.
On the other hand, takeoff is the second most dangerous phase of flight. During the takeoff roll, as the speed of the aircraft is increasing, the pilot is supposed to decide more quickly and react more precisely in case of an emergency.
In this essay, I want to talk about the importance of decision making by pilots during takeoff run in case of an abnormal situation; whether to continue takeoff or to reject it and to discuss the standards according to which pilots must decide GO/NO GO.
Takeoff rejections or a pilot’s decision-making ability to go or not to go during an abnormal situation arising in takeoff run is one of the areas of concern in the safety of takeoff. Pilots may perform high-speed rejects unnecessarily or may not perform the rejected takeoff procedure properly. The airlines, manufacturers, and other related agencies have been working together to improve takeoff safety.
According to National Transport Safety Board (NTSB) investigation report, runway overruns following high-speed rejected takeoffs (RTOs) have resulted and continued to result in airplane accidents and incidents. In a more detailed discussion, Boeing analysis shows that about half of the overrun accidents and incidents resulted from a rejected takeoff initiated after V1. As you know, V1 is the fundamental speed during takeoff roll according to which we must decide whether to take off or to abort takeoff and stop the aircraft (GO/NO GO decision). If a pilot rejects the takeoff before reaching V1, he or she will be able to stop the aircraft to the end of the runway, but if the pilot delays his or her decision for just two seconds, he or she will not be able to stop the aircraft until the end of the runway. Now, let’s take a look at how this V1 speed is calculated by manufacturers at first.
During certification test of the aircraft, they measure takeoff performance over a wide range of thrust-to-weight ratio and environmental conditions. They continue takeoff for several times, following an abnormal situation like engine fire, and the test pilot is required to maintain directional control and smoothly rotate to a target body attitude. On the other hand, they also test accelerated stop test by maximum braking at V1, bringing the thrust levers to idle and raising the speed brakes at about one second later. The test pilots don’t use thrust reverse in testing, so there will be an added choice for airline pilots in such a situation.
Because the airline pilots do not know when and if the reject will occur, an additional two seconds distance is added. This two seconds gives the airline pilot additional time to get the aircraft to full-stop configuration.
After this flight test, engineers analyze the data. Then they produce easy-to-use operational charts and tables according to that data for pilots. Now that we know V1 and the importance of that in takeoff safety, let’s take a closer look on how speed relates to reasons of rejecting takeoff.
For example, at low speeds, it is logical to reject takeoff due to system failures, unusual noise or vibration, tire failure, abnormally slow acceleration, engine failure or fire, unsafe takeoff configuration warning or the perception that the airplane is unable to fly. We must always remember that if we have not applied brakes before V1, we have decided to takeoff. According to statistics, engine failure is the first reason for takeoff rejection. After that, comes wheel or tire problems, problem with configuration, indication and light, crew coordination, and bird strikes. Although engine failure was the first reason, about 76 percent of the rejected takeoffs were due to non-engine related problems, and the aircraft had sufficient power and thrust to take off. So why did the pilots prefer to reject?
For example, tire failure has become a matter of concern. Some pilots think of tire failure as a factor threatening the flying ability, and as a result, do an unnecessary reject. In some cases, the tire failure may cause its pieces to be thrown against the aft body or flaps, but it is usually not going to affect the ability of aircraft to fly. Boeing recommends, “Unless a tire failure in the high-speed regime has produced damage that puts the ability of the airplane to fly in serious doubt, the takeoff should be continued.”
Both GO or NO GO decisions have their own complex events. For example, in one real accident report, the pilot decides to reject takeoff after V1. In that accident, the first officer was doing the takeoff, and he confirmed that in case of an emergency during takeoff, the captain would make the decision to reject, and the first officer would do it. After 1.5 seconds after V1, on call out of 156KTS, engine number four-fire warning came on. In the cockpit, the first officer mentioned that he noticed the movement of the captain’s hand toward the throttle and thought he should reject takeoff and did it, but the captain did not make any call out to reject. The airplane couldn’t be stopped during the paved available runway and finally came to stop out of the runway. The aircraft was damaged substantially and the fact was that there was not a fire.
Takeoff reject after V1 and lack of crew coordination were the probable causes of this accident. There are also a few points that are better to be taken into consideration before a safe takeoff. For example, to calculate the last minute changes in the weight of the aircraft, runway condition, wind, and runway length. When you are instructed to taxi the aircraft into the runway, it is better to position the aircraft as near to the end of runway as possible. Don’t delay setting takeoff thrust. The sooner you set it, the more runway you will have if you need to stop your aircraft.
Although takeoff reject after V1 is at the full authority of the captain, as mentionثیptain, but as mention beforeaptain, but as mention beforere runway you will have if you need to stop your aircraft.ircraft as ed before, Boeing recommends that the takeoff shouldn’t be rejected unless there is a serious doubt about the ability of the airplane to fly. It is normally best continue takeoff and deal with the problem in the air.
There are advantages of GO decision over NO GO decision during a takeoff roll abnormal situation:
1. Gross weight reduction of the aircraft and the chance of burning fuel––on-board while in the air.
2. The crew is more prepared for the emergency, and the pilot has a better directional control over the aircraft.
3. The crew has more time to analyze the problem in the air.
4. During the landing, there will be more runway available to the aircraft.
5. The pilot will be able to use landing flaps for speed reduction.
Pilots are required to prepare themselves completely for different kinds of emergencies, including takeoff reject in simulators. The more practice in simulators, the more they are prepared for the real emergencies.
At the end, we can conclude that takeoff reject like other cases of emergencies require well-prepared crew and good training. As mentioned before, the GO or NO GO decision should be made long before the V1, and at the V1 is not the time. In takeoff reject, early detection of the problem, good crew coordination, and quick reaction are the fundamental keys to a successful reject.
