Issue # 2002-2
National Transportation Safety Board (NTSB) noted that in 1999, the
ORD (CCA9018/KAL036), JFK (ICE614/AFR6498), and LAX (AMX432/UAL204)
runway incursion incidents involved flight crews whose primary
language was not English. Based on these incidents, the NTSB
recommended that controllers speak at reasonable rates when
communicating with all flight crews, especially to those whose primary
language is not English. International pilots may have difficulty
comprehending air traffic control (ATC) instructions that are not
communicated at reasonable speech rates. To minimize chances for
misunderstanding instructions, we encourage controllers to speak at
reasonable rates when communicating with all flight crews. (ATP-120)
The following is a description of a serious situation that could have become a tragic accident. As you read through the summary, take a moment to consider whether you could have been caught in the same trap. The most valuable lesson is one that can be learned without having to go through bitter experience to do so.
THE FRAMEWORK FOR AN ACCIDENT
and 29L cross each other and were both active. Taxiway Charlie runs
parallel with runway 29L and is located on its south side.
N9231C, a PA28
Local control instructed N9231C to taxi into position and hold on runway 22 because another aircraft was departing on runway 29L. Meanwhile, N75231 had completed his preflight run up check and was ready to depart on runway 22 from the intersection of runway 22 and taxiway Charlie. The local controller responded, "N231 runway 22 intersection Charlie cleared for takeoff."
of N9231C and N75231 both responded to the clearance simultaneously
and N9231C got airborne first. When the controller saw it, the
aircraft's nose wheel was leaving the ground. The controller was able
to stop N9231C's takeoff in
order to avoid a collision, and the pilot was able to stop his
aircraft 900 feet behind N75231.
WHAT HAPPENED? WHO WAS AT FAULT?
Obviously, N9231C took the clearance intended for N75231. However, if we look at the circumstances of this incident carefully, we can see how the links in the chain of events were built, and how, although inadvertently, ATC aided the process.
Notice the similarity and coincidence of the call signs themselves: N231Charlie and N231. Both call signs contain the numerals, 231. The word, "Charlie," is connected to both aircraft, although in different ways. "Charlie" is part of the aircraft's call sign for one aircraft, and for the other aircraft, "Charlie" is its location on the airfield. Both aircraft are the same type.
Now let's look at the situation from the point of view of the pilot of N9231C. He has been instructed to taxi onto the runway and wait there due to a departure off runway 29L that will cross runway 22 downfield. By putting the aircraft into position on the runway, two expectations have been built – – first, that takeoff clearance is being withheld only momentarily, and second, that as soon as the runway 29L departure is through the intersection, takeoff clearance can be expected to follow. In other words, the next thing the pilot expects the controller to say is, "cleared for takeoff," not an unreasonable expectation if you think about it.
However, from the controller's point of view, the situation is quite different. One aircraft is not going anywhere because it is holding in position on the runway. The other aircraft is ready to go at the intersection. With the runway 29L departure out of the way, there was an opportunity to quickly get the intersection departure airborne, and the controller decided to take advantage of that opportunity.
The controller inadvertently set a trap for the pilot holding on the runway. Here is an analogy to explain what we mean.
Sprinters are lined up at the starting line for a foot race. The starter calls out, "Ready…Set…Joe, get that dog off the track!" Do you think any of the runners would still be poised waiting for the word, "Go?" I doubt it. Most likely all would have started off the blocks as fast as they could run. This is what happens when a person is primed for a certain expectation.
In the case of the two pilots, the pilot holding in position had been primed to expect takeoff clearance after the runway 29L departure was out of the way. In addition, the curious combination of call signs, aircraft types, and the word, "Charlie," made it much easier for the pilot to believe that the clearance was intended for him. The other pilot, N75231, may or may not have been aware of N9231C holding in position, but even if he was, the clearance was clearly directed to his aircraft and his expectation obviously was that the holding aircraft would continue to hold.
HOW DO WE PREVENT
SUCH NEAR DISASTERS?
Part of being successful in this business is cultivating the ability to analyze situations quickly and accurately to stay ahead of the game. Try to be alert to situations where mistakes can be made. Think to yourself, "What is the worst thing this pilot could do right now to mess me up or cause an incident?" If you can do that and prepare so that it can be avoided, then your career as an air traffic control specialist may be blissfully uneventful.
THE PILOT SAID
Pilots are required to inform ATC when navigation, approach, or communication equipment malfunctions occur during flight (CFR 91.187). This announcement makes sense because the aircraft's ability (or inability) to navigate, directly affects the controller. If the aircraft's sole VOR receiver quits working, then the aircraft will not be able to navigate on Victor or Jet airways. Unless the aircraft has a backup navigation system, the flight will be dependent upon the controller for navigation assistance in the form of radar vectors. And once the aircraft is ready for an approach to its destination, it would be silly to issue a VOR approach, wouldn't it?
Although not required, sometimes pilots will share information with you regarding other instrument or mechanical failures. What does that mean to you? The pilot's mention of the loss could be a signal to you that the aircraft may soon enter into an emergency status, or require a little different handling, or may require no change to your operation at all. Often, the loss or malfunction of an aircraft component is more or less transparent to you, the controller, whereas it is a slightly bigger deal for the pilot.
An announcement that the aircraft's electrical system is compromised by the failure of the alternator or generator means that the loss of the aircraft's radios, transponder, and some navigation equipment will probably follow (if it has not already occurred). Depending on the aircraft, emergency battery power or air powered turbines may take up the slack for a short period of time, but if it happens to a small general aviation type aircraft, both you and the pilot soon will be in the dark. Consider electrical problems a potential emergency. Prepare to block airspace for a "NORDO" aircraft and consider what actions the pilot may take. If the aircraft is in instrument meteorological conditions (IMC), it will continue to fly its last assigned route, if it is able, but if it encounters VFR conditions, it may change course and proceed to the nearest airport. Pay attention because if the aircraft has no electrical power, its transponder will not be working. This means primary target only for radar controllers, and losing track of an IFR primary target can cause a lot of trouble.
WHEN THE PRESSURE
Hydraulic power systems are associated with jet and turbojet aircraft. Small, general aviation aircraft do not rely on hydraulic systems to operate their flaps and flight control surfaces. The loss of hydraulic pressure affects an aircraft's ability to deploy flaps. This translates into higher approach speeds and longer runway rollouts. Give the aircraft more room for descents and make certain you set the aircraft up for a stable approach for landing. High, short approaches are very much counter productive in these cases! Be aware that the aircraft may not be able to taxi off the runway due to loss of nose wheel steering on the ground. In that case, it will need to be towed to its destination.
LOOK MA, NO WHEELS!
Gear up landings are generally not life threatening. They are damaging in varying degrees to the aircraft, but its occupants usually enjoy just a noisy slide down the runway. However, that being said, always treat a gear up landing as an emergency because there is always the chance that a wing tip may get too low and drag during the approach. If this happens, there is a chance that the aircraft may cartwheel out of control or slide off the side of the runway and hit whatever is there to hit. If the pilot had misjudged and comes in too high and fast, there is also the possibility that the aircraft will go off the end of the runway. You can help by providing a stable approach to the runway. Again, short, high, fast approaches are not helpful to the pilot.
If a pilot informs you that the aircraft's vacuum system has failed, what does this really mean? What can you expect? Is this just "nice-to-know" information? We have an accident on record where a pilot informed the controller that the aircraft's vacuum system had failed. The controller duly passed on this information to the next controller, stating that the aircraft's vacuum cleaner had quit or something like that. Whether this was an ill-timed attempt at humor or an honest misinterpretation is hard to say, but it was clear that neither controller understood the seriousness of the pilot's predicament. You may not be able to do much about the difficulties the pilot is having, but there are some things to keep in mind that will help you avoid aggravating the situation. And yes, the loss of the vacuum system is serious for the pilot.
The attitude indicator is THE primary instrument, and its loss is serious. The ability to control the aircraft in IMC conditions without the attitude indicator is problematic, especially if turbulence is added to the equation. When a pilot reports a loss of vacuum, this is the instrument that is usually affected.
A pilot can control the aircraft by reference to only three instruments during IMC conditions. Those three instruments are the turn and slip indicators and the airspeed indicator. Controlling the aircraft with only the three instruments (referred to as needle/ball/airspeed) is difficult, takes a lot of concentration, and is very fatiguing. It is a true emergency situation.
Normally, the pilot will rely upon the following instruments to keep the aircraft under control:
Attitude Indicator/Artificial Horizon: This is a gyroscopic instrument powered by the aircraft's electrical system or by a vacuum pump. It enables the pilot to keep the aircraft right side up. The instrument is almost always powered by a vacuum pump in the general aviation fleet.
Heading Indicator/Directional Gyro (DG): This is a gyroscopic instrument powered by the aircraft's electrical system or vacuum pump. It provides the pilot with an easy to read, steady display of the aircraft's heading. However, the heading indicator creeps and must be reset with the magnetic compass about every 15 minutes. More expensive gyros are connected with a magnetic compass in such a way that the tendency to creep is automatically corrected. This instrument does not have the oddities that plague the magnetic compass.
Turn/Bank and Slip Indicator (two instruments in one): The turn indicator (needle) is a gyroscopic instrument powered by the aircraft's electrical system or vacuum pump. The needle uses precession to indicate the direction and approximate rate of turn of the aircraft. This instrument helps the pilot execute standard rate or half-standard rate turns. The slip indicator (ball) reacts to centrifugal/centripetal forces exerted on the aircraft. This instrument helps the pilot coordinate the input of the aircraft's rudder and ailerons during turning movements. Both instruments help the pilot execute coordinated turns. The instrument is almost always powered by the aircraft's electrical system in the general aviation fleet.
Altimeter: The altimeter is affected by atmospheric air pressure. This instrument tells the pilot how high the aircraft is above sea level.
Airspeed Indicator: The airspeed indicator is affected by ram air pressure. It is an air pressure gauge calibrated to read in miles per hour or knots instead of pounds per square foot.
Vertical Speed/Rate of Climb Indicator: This instrument is affected by air pressure. It indicates the rate of climb or descent the aircraft is making. Pilots may use the instrument to maintain a particular rate.
Magnetic compass: The magnetic compass is affected by acceleration/deceleration, northerly turning error, magnetic variation and magnetic deviation. Although more difficult to use, this instrument can provide reliable information on what direction the aircraft's nose is pointing.
Other than the altimeter, airspeed indicator, and turn/bank indicator, small, general aviation aircraft gyro instruments are typically powered by an engine-driven vacuum pump or combination of pump and electrical system. If the pump fails, those instruments dependent upon the pump for power will cease to operate. Conversely, if the aircraft's electrical system fails, then electrically driven instruments will cease operation. Most single-engine general aviation aircraft do not have backup systems, that is, the instrument is powered by either the electrical system or the vacuum system, but not both.
So, how can you help? If the pilot advises that a loss of the vacuum or electrical system has occurred, ask the pilot whether or not assistance is needed. If the answer is "Yes," here are some points to keep in mind.
First, do not jump right into issuing the pilot turns! Let the pilot fly straight ahead. If there is traffic in the way, move it. If the aircraft is approaching your airspace boundary, coordinate with the neighboring controller for its use. Do not issue turns until the pilot indicates that he/she is ready and able to turn the aircraft. Of course, if the aircraft is approaching terrain or obstructions, you have no choice but to warn the pilot and suggest a turn to avoid a collision.
Try to get the aircraft to VFR conditions. If a climb or descent is necessary, establish the aircraft on a heading before beginning the change in altitude. Try to avoid issuing altitude changes concurrent with changes in heading while the aircraft is in IMC. As stated before, the aircraft can be managed with the three basic instruments, needle, ball, and airspeed, but it is difficult. Pilots are required to master "partial panel" control of the aircraft using only the three instruments and the aircraft's altimeter and must demonstrate this ability to the flight examiner in order to pass the instrument flight test to acquire the instrument flight rating. The skill necessary to achieve success is obtained only after much diligent practice, but, once the rating is attained, few pilots ever practice partial panel control of the aircraft again, so the skill is pretty much lost.
Keep your instructions short and brief. That is, do not issue a string of commands or questions. Remember, the pilot has to exert a lot of concentration to keep the aircraft right side up. Also, an autopilot is useless in this case because it uses the gyro instruments for guidance just as the pilot would if they were working!
So if a pilot tells you that the aircraft's
vacuum system is kaput, now you will have a little better idea of what
is going on, and what problems the pilot may be facing… and that it
is not a cleaning problem! (AAT-200)