Specific Flight Characteristics

Only conditionally: the evaluator only tests this Task if the airplane has specific flight characteristics identified in the Flight Standardization Board Report (FSBR) (FAA-S-ACS-11A, App. 3). If it is tested, the skill element requires proper techniques, checklists, and procedures to enter into, operate within, and recover from the specific flight situations (AA.IV.C.S1) — meaning the demonstration is flown from your type's published procedure, not improvised. The knowledge element is deliberately open-ended: all specific flight and performance characteristics associated with the aircraft (AA.IV.C.K1).

The FSB report is the FAA's type-specific training document; the UPRT and stall-prevention ACs both direct carriers to consult the FSB report, if available, for the specific airplane type when building training programs, and to review its Training Areas of Special Emphasis and any other recommendations on in-flight handling (AC 120-111, para 3-2b; AC 120-109, para 2-6). For this Task the FSBR is literally the exam blueprint — it is the document that decides whether the Task is tested at all and which characteristic gets flown (FAA-S-ACS-11A, App. 3).

A nose-down pitching tendency in the transonic range, caused principally by:

1. Shock-wave-induced flow separation — beginning normally near the wing root, it decreases the downwash velocity over the elevator, producing a nose-down tendency
2. Aft movement of the center of pressure — the CG ends up farther ahead of the aerodynamic center than in slower flight, dramatically increasing the nose-down pitch tendency (AC 61-107, para 3-2)

Mach tuck develops gradually; the condition must not be allowed to progress to where there is no longer enough elevator authority to prevent entry into a steep, sometimes unrecoverable, dive — respond to excessive airspeed, buffeting, or warning devices before extreme nose-down forces set in (AFH ch. 16).

Most jets capable of Mach-range flight use automated Mach tuck compensation (Mach trim); if the system is inoperative, the airplane is typically limited to a reduced maximum Mach number (AFH ch. 16). Separately, types operating near MMO carry a trim/autopilot Mach compensating device — a stick puller — to alert the pilot to excursions beyond certificated MMO; if a malfunction requires disabling it, the aircraft must be operated well below MMO per the AFM, and the AC is emphatic that the stick puller should never be disabled in normal operations (AC 61-107, para 3-2). Your type's specific system and its MEL/AFM penalties are the answer the evaluator wants.

Mach buffet is airflow separation on the upper wing surface behind a shock wave — it is a function of the speed of the airflow over the wing, not necessarily the forward speed of the airplane, and the shock wave strength, rather than a stall, creates the separation (AFH ch. 16). It appears in two cruise conditions: at high-speed cruise, an overly strong shock; at low-speed cruise, high AOA accelerates the flow over the upper surface past Mach 1 locally, and the separated flow acts over a larger portion of the chord, with a more significant effect on control (AFH ch. 16). A buffet at altitude could be your first indication of a problem — you must know which side of the envelope it is coming from to respond correctly.

Coffin corner, the aerodynamic ceiling, is the altitude where the low-speed buffet boundary IAS and the high-speed Mach limit converge, as increasing altitude drops IAS relative to TAS: fly any faster and you exceed MMO into high-speed Mach buffet; fly any slower and the required AOA brings low-speed buffet (AFH ch. 16). At that point the airplane can neither go faster without activating the stick puller nor slower without activating the stick shaker or pusher (AC 61-107, para 3-2). This region carries loss-of-control consequences, which is why cruise altitude selection must preserve buffet margin.

Increasing gross weight or G-loading raises the low-speed buffet speed and lowers the Mach buffet speed at once. The AC's example: a turbojet at 51,000 feet and 1.0 G with MMO 0.82 may see Mach buffet slightly above MMO and low-speed buffet at 0.60 Mach — but only 1.4 G brings buffet on at the optimum 0.73 Mach, and any change in airspeed, bank angle, or gust loading can reduce that protection to none (AC 61-107, para 3-2). Mitigations:

• Select a maximum cruising altitude that leaves buffet margin for maneuvering and gusts
• Use the cruise maneuvering/buffet limit charts
• Know the manufacturer's turbulence penetration speed, which normally gives the greatest margin between the buffets (AFH ch. 16)

• Lift builds more gradually with AOA, with a less well-defined maximum — so the loss of lift past the peak is less dramatic, but the high-lift condition brings high drag and possibly a high rate of descent (AFH ch. 16)
• An unmodified swept wing tends to stall at the tips first because the boundary layer flows spanwise toward the tips; tip stall lets the center of lift move forward (a pitch-up tendency), worst when sweep and taper are combined (AFH ch. 16)
• Manufacturers counter with twist, airfoil-section changes, and vortex generators so roll control survives an inadvertent stall entry — and airplanes without vortex generators may stall with little to no buffet (AFH ch. 16)

Some T-tail configurations can reach a stall where the tail is immersed in the wing wake at very high AOA and loses effectiveness, possibly with a high descent rate. Since high AOA can occur at any pitch attitude — even nose below the horizon — the correct recovery, pushing the nose down further, may seem counterintuitive. Deep stalls may be unrecoverable, but they are easily avoided by observing published limitations; susceptible types carry stick shakers as standard, and a stick pusher automatically reduces AOA before a dangerous stall condition, or aids recovery where natural aerodynamic recovery is weak (AFH ch. 16). Avoid situations that would fire the pusher close to the ground.

A coupled oscillation in roll and yaw that becomes objectionable when roll (lateral) stability is reduced relative to yaw (directional) stability. Certification requires a stability augmentation system where the tendency is objectionable or adversely affects control stability — the yaw damper, a gyro-operated system providing rudder inputs to cancel the yaw (AC 61-107, para 3-3). On swept-wing airplanes the yaw damper's ride-smoothing function is secondary; damping Dutch roll is the more vital function (AFH ch. 13). Know your type's dispatch and handling implications with the yaw damper inoperative — that is exactly the kind of item an FSBR flags.

Speed instability is what the AFH calls one of the most important aspects of jet-airplane flying: a jet's minimum-drag speed (VMD) is typically 1.5–1.6 VS — well above a piston airplane's well-identified 1.3 VS — and flight around it produces no obvious change in feel except a lack of speed stability. A decrease in speed increases drag, which decreases speed further: a potential speed divergence. A pilot unaware of the divergence can develop a serious sink rate at a constant power setting while the pitch attitude appears normal (AFH ch. 16).

Reduced density means CAS is much slower than TAS, and AOA must increase to maintain the same lift coefficient with altitude — so a jet at high altitude and high Mach can simultaneously experience slow-speed problems: Dutch roll, adverse yaw, and stall. The thin air also reduces aerodynamic damping, overall stability, and control (AC 61-107, para 3-3). Design features — swept wings, tailored airfoils, vortex generators as boundary-layer energizers — reduce but do not eliminate these behaviors in the modern turbojet (AC 61-107, para 3-3).

Three linked effects (AC 61-107, para 3-3):

• Shock waves forming on the wing — drag rise
• Aft shift in the center of lift — the nose-down pitching moment called Mach tuck
• Airflow separation behind the shock waves — Mach buffet

One shock wave, three symptoms — the oral answer that connects them beats three memorized definitions.

Work from the documents the ACS itself references: the FSB Report (type specific) and the POH/AFM (FAA-S-ACS-11A, Task IV.C references). Build your list from three places:

• The FSBR's Training Areas of Special Emphasis and handling recommendations (AC 120-111, para 3-2b)
• The AFM's limitations and non-normal procedures tied to the characteristics above — Mach trim, yaw damper, stall protection systems
• Your program's maneuver profiles for entering, operating within, and recovering from each characteristic, since the skill element grades checklist and procedure use (AA.IV.C.S1)

The risk element pairs each characteristic with its effects and applicable procedures (AA.IV.C.R1) — for every item on your list, be able to say what it does to the airplane and which procedure answers it.

These characteristics announce themselves through warnings — buffet, stick shaker, stick puller, overspeed cues — and a pilot in such an event can be rapidly confronted with multiple or simultaneous visual, auditory, and tactile warnings, while an expected warning that doesn't fire can distract a pilot as much as multiple warnings can (AFH ch. 5). Separating the time-critical information from the distractions takes practice, experience, and knowledge of the airplane and its systems, plus a cross-check that catches missing or invalid cues — a failed stall warning still leaves buffet, loss of roll authority, and an unarrested descent as tells (AFH ch. 5). Task-prioritize accordingly: the margin of safety is task requirements versus pilot capabilities (AFH ch. 5) — fly the airplane first, run the associated non-normal procedure second.