/*T/ FAAO 7110.65 Air Traffic Control, paragraphs 3-9-5 and 3-10-6, provide for the application of anticipated separation for departures and arrivals. A takeoff or landing clearance need not be withheld if the prescribed runway separation will exist when a departing aircraft starts its takeoff roll or when an arriving aircraft crosses the landing threshold. The determination that prescribed runway separation will exist is based on positive control through the issuance of specific instructions to ensure that crossing traffic or other aircraft will not be factors for the landing or departing aircraft.
In correctly applying anticipated separation, a controller must recognize that pilots are listening on the frequency and may try to second-guess the controller’s intentions if the intentions are not clearly specified. In a recent incident, a controller had assumed that an arriving aircraft landing on a crossing runway would roll through the intersection prior to the time that the departing aircraft on the crossing runway began its takeoff roll. No instructions were issued to the landing aircraft to proceed through the intersection or to turn off the runway at any particular exit. As a result, the pilot of the landing aircraft, upon hearing the issuance of the takeoff clearance to the departing aircraft, applied heavy braking and tried, unsuccessfully, to stop short of the intersection.
It must be emphasized that the above example constitutes an inappropriate and incorrect application of anticipated separation. Action was not taken to ensure that the aircraft would roll through the intersection prior to the time that the departing aircraft began its takeoff roll or exited the runway at a specified point prior to reaching the intersection. A correct application of anticipated separation is predicated on the issuance of specific instructions with acknowledgements, if appropriate, so that the controller can ensure that all potential conflicts will be resolved and that all pilots understand and have acknowledged their instructions.
As the example highlights, basing separation on assumed actions of pilots may lead to undesirable results. In conclusion, anticipating separation is not assuming that separation will exist; anticipating separation is exercising positive control actions to ensure that the prescribed separation will exist. (ATP-120)
Vectoring VFR Aircraft
/*T/ FAAO 7110.65, Air Traffic Control, paragraph 5-6-1, requires that aircraft be vectored at or above the minimum vectoring altitude (MVA) or the minimum IFR altitude (MIA) except VFR operations, or by paragraph 5-6-3, Vectors Below Minimum Altitude. Paragraph 4-2-8, IFR-VFR AND VFR-IFR FLIGHTS, allows a controller to issue an IFR clearance to a VFR aircraft below the minimum altitude for IFR operations unless the controller is aware that the aircraft is unable to climb in VFR conditions to the minimum IFR altitude.
VFR aircraft not at an altitude assigned by ATC may be vectored at any altitude. A controller may assign an altitude to a VFR aircraft, but altitudes assigned must be at or above the MVA/MIA. A pilot operating under VFR climbing to an altitude assigned by ATC is responsible for maintaining appropriate terrain and obstruction clearance. (ATP-100)
Now Who Wouldda Thought…
We all know what wake turbulence is. Those who provide air traffic services to large, heavy, and B757 aircraft know what longitudinal separation standards must be applied. Most of us understand that the danger associated with wake turbulence is loss of control, primarily roll control. The vortices associated with wake turbulence are of such strength that an aircraft traveling behind the aircraft generating the wake can be forced into a roll from which it cannot correct or recover. However, most controllers, thankfully, have not observed the effect of wake turbulence and the damage it can inflict upon the unwary. What some controllers are not aware of is the consequence of a wake turbulence encounter perpendicular to the flight path of the wake-generating aircraft.
An aircraft flown across wingtip vortices will encounter rapid pitch changes. When the encounter takes place at a time when the vortices have had a chance to dissipate somewhat, the encounter feels very much like hitting a large pothole or "speed bump" at 60 mph in your car. However, given the right circumstances (or wrong set, depending upon your point of view), if the encounter takes place very soon after the vortices have been generated, when the vortices are still powerful, the sudden noseup then nosedown forces on the aircraft can cause severe structural damage to the aircraft. In some instances, this damage may be severe enough to compromise the ability of the aircraft to continue flight.
A wake turbulence encounter perpendicular to the wake-generating aircraft occurred during the month of September. A Piper Navajo (PA31) flew a flight path perpendicular and 2.47 NM behind and 300 feet below an MD-11. The pilot was able to land the aircraft, but it had suffered substantial damage during its wake turbulence encounter. As of this writing, internal damage assessments have not yet taken place, but upon examination, obvious damage was as follows: wrinkling of the right outboard wingtip skin, wrinkling of the right wing skin midspan (from engine nacelle to wingtip), severe damage to the right winglet, loss of right landing light, slight wrinkling of left wingtip skin, and wrinkled skin damage to the horizontal stabilizer. Aircraft of this category are stressed to withstand positive G loads of +3.8 and -1.52. In order to deform an aircraft’s skin, substantial G loading above normal must be experienced. The internal damage to the aircraft may include twisting/deformation of wing ribs, spar, and fittings.
Respect the power of wake turbulence and apply wake turbulence separation standards at all times. Whether the aircraft is following or crossing the wake-generating aircraft’s path, issue wake turbulence advisories to pilots as required. (AAT-200)