SLOW FLIGHT

Aim

Students must demonstrate the ability to establish the aircraft in flight near minimum controllable airspeed as indicated by a near-constant stall warning or aerodynamic buffet, to maintain flight control, to manoeuvre, while preventing a stall, at that speed and to recover promptly and smoothly to normal flight on command. 

Description

At an operationally safe altitude that would allow recovery from an inadvertent stall at or above 2,000 feet AGL or the minimum altitude recommended by the manufacturer, whichever is higher, the candidate will establish and manoeuvre the aircraft in flight near minimum controllable airspeed.  Airspeed may be increased slightly during a turn or in turbulent conditions.  A slight increase in airspeed while turning or in turbulence is acceptable as the stall speed increases in these conditions.

Performance Criteria

Private Pilot Students must:

  • complete appropriate safety precautions before entering slow flight;
  • maintain an effective lookout;
  • establish and maintain the aeroplane in flight near minimum controllable airspeed as indicated by a near-constant stall warning or aerodynamic buffeting, with an aircraft configuration appropriate for that speed range;
  • demonstrate coordinated straight and level flight and a level turn, with an angle of bank of 15° in flight near minimum controllable airspeed;
  • divide attention between aeroplane control and orientation;
  • maintain specified altitudes (±100 feet), headings (±15°) and angles of bank (±5°);
  • roll out on specified headings (±15°);
  • prevent a stall and, on command, recover promptly and smoothly to normal flight.

Commercial Pilot Students must:

  • complete appropriate safety precautions before entering slow flight;
  • maintain an effective lookout;
  • establish and maintain the aeroplane in flight near minimum controllable airspeed as indicated by a near-constant stall warning or aerodynamic buffeting, with an aircraft configuration appropriate for that speed range;
  • demonstrate coordinated straight and level flight and a level turn, with an angle of bank of 15 degrees in flight near minimum controllable airspeed;
  • prevent a stall;
  • maintain specified altitudes (±100 feet), headings (±10°) and angles of bank (±5°);
  • roll out on specified headings (±10°); and
  • on command, recover promptly and smoothly to normal flight.

Note:  Avoid prolonged periods in slow flight so as to avoid possible engine overheating.

Discussion

A HASEL check must be conducted before the manoeuvre.

HASEL is an acronym for Height, Area, Security, Engine, and Lookout.  It is a short vital-actions checklist that must be performed prior to the following manoeuvres: stalls, spins, slow flight, and spirals.1

Failure to perform the HASEL check is a serious safety violation and will constitute a failure on the flight test.

Remember, the flight test Examiner will not remind you to perform the HASEL check; the student pilot must instead demonstrate awareness.

Height

Do you have sufficient height to perform the manoeuvre safely?

For stalls, spins and spirals you are legally required to recover above 2000’ AGL (above ground level) or a height recommended by the aircraft manufacturer (prescribed in the Pilot’s Operating Handbook), whichever is the greater.  In the case of the Piper Cherokee, the handbook requires recovery by 3000’, so this governs.  When stalls are performed, you must always assume that you might inadvertently enter a spin, and select your initial altitude accordingly.  Additionally, when you perform spins you must assume delayed recovery (3 to 5 revolutions) and also judge your initial altitude accordingly.  For spirals, a 1000’ descent should be planned.  The HASEL check for practising slow flight is protection against stalls and spins during the manoeuvre.

Area

Ensure you are in the practise area and are not over built-up areas or obstacles (antenna).

Security

Security in the cockpit.  Ensure the fire extinguisher is secure—physically check to ensure the extinguisher is attached.  Are all other objects secured in the cabin?  Are the rear seats secured by their seat belts?  Ensure also that seat belts are tight—a person coming out of a harness during manoeuvres can kill.2  Ensure the flaps are retracted.

Engine

Perform a left-to-right “downwind check,” including a carburettor ice check, fuel check, engine gauges, fuel mixture, and flaps set.

Lookout

Using an angle of bank no greater than 30°, perform either one 180-degree turn, or two 90-degree turns in opposite directions.  Whether you use one 180-degree turn or two 90-degree turns will depend on your position in the manoeuvre area (i.e., the practise Area).  You must visually ensure that the airspace below, around, and above, is clear of other aircraft.3  Concentrate on the airspace you plan to use during the manoeuvre.  Once the lookout is completed, proceed immediately into the manoeuvre while the airspace is still clear.  While performing HASEL checks, be disciplined with respect to your altitude and heading.  Develop the habit of working a specific altitude, and when your clearing turns are completed, return to and maintain a specific heading using the north/south, east/west road system.  This is a sign of an advanced pilot.

 

To enter, reduce power to a landing approach setting (1700 RPM).  Smoothly add partial flap once below the white line (airspeed indicator)—25° or two notches.  Allow the aircraft to slow to the target speed, and then, just before the target speed is reached, adjust power to maintain altitude and airspeed (2000 RPM is a good starting point).The HASEL check must precede each series of manoeuvres.  Before each manoeuvre, since height, area, security, and engine will likely not change, a lookout must be performed (see above).

Procedure

Slow flight entry procedures.  Langley Flying School.

The performance criteria for slow flight require keeping the aircraft within 100’ of the target altitude.  In this regard, the transition from normal flight to slow flight is crucial, and this is where most flight test candidates have problems.  The secret is to be smooth with control and power inputs, and anticipate that you will have to use timely pitch changes to maintain level altitude (as airspeed is reduced).  As airspeed slows, closely watch the altimeter and use this instrument as the primary reference for pitch, making adjustments by carefully watching and adjusting the position of the nose relative to the horizon.  As you decelerate to slow-flight speed, trim becomes critical, so you want to take the time to make appropriate and continuous trim adjustments until the power is increased to maintain the constant slow-flight speed.

Whatever you do, never . . . never . . chase the airspeed indicator. It is crucial to concentrate on the detailed position of the nose relative to the horizon as only careful control and attention here can maintain a constant stall warning indication. The nose must be held constant and moved in small increments. Practice makes perfect in all flying, but especially in slow flight.

Also, throughout this manoeuvre, make sure to keep the aircraft tracking straight—in this respect, it is crucial to use a prominent reference point to line up the nose of the aircraft, and remember that the nose will yaw to the right as power is reduced.

Slow Flight Flight Test Limits. Langley Flying School.

Trim is important.  So are the rudder inputs—as you reduce the power you must keep the nose going straight with your feet (the smoother you are with the throttle changes, the easier the footwork is).

In slow flight you will be required to demonstrate climbs, descents, and turns; accordingly, during climbs, full power is always selected, and of course you will have to demonstrate the associated control of yaw (which is pretty intense during slow flight).  Be sure that a geographic reference is used to ensure the aircraft is not allowed to stray off its initial heading.  You will notice that the ailerons become mushy, and that effective and aggressive use of rudder will be required (be sure to keep the ball in the centre at all times).  Learn to master controlled turns during slow flight.

As a rule, only standard-rate4 turns are used in slow flight (remember that standard rate turns are indicated by markers on the turn co-ordinator, or can be calculated (angle of bank, that is) by taking 10% of your airspeed and adding 5 (MPH) or 7 (KNOTS).  The maximum turn to be performed during slow flight is 30° of bank, at which time considerable power will be required to maintain altitude and airspeed.5  Notice that the 30°-banked slow-flight turn is also the “minimum radius” turn.  Practise especially the entry into slow flight and the recovery from slow flight—these are the most difficult phases.  Be sure to keep a constant altitude and heading as the yaw and pitch changes are extreme.  To recover, smoothly apply power by setting the cruise power settings (2300 RPM, for example) and smoothly resuming cruise attitude (using the altimeter for pitch references).6  As airspeed increases, slowly recover flaps (do not forget), but make sure you compensate for the loss in altitude as the flaps are being recovered by adding pitch upward.7  Watch your altitude and speed tolerances at all time; while you must scan for traffic during slow flight, periodically scan your airspeed indicator and altimeter.

Flight Safety

  • HASEL check.  Altitude should be high enough to recover from a stall—i.e., 2000’ above ground minimum, or as prescribed by the Pilot Operating Handbook.
  • Be conscious of blind spot below the front cowling.  For this reason, if able, regularly change your heading to clear the cowling area.
  • Special caution must be taken with respect to the 30°-banked slow-flight turns owing to the radical change in direction and the risk of collision; check for traffic first in the opposite direction to the turn, and then check for traffic in the direction of the turn.
  • Prolonged slow flight will cause excessive engine heating.

References

1 Students often get confused and believe that a HASEL check must be performed before steep turns—this is not the case, although an effective lookout is required on both sides of the aircraft.

2 Checking the seatbelts must be accomplished by physically tugging on the belts—this can be politely accomplished by tugging the belt near the floor mounts between the seats.

3 Some students become so overly concerned with traffic and the fear of encountering another aircraft during the performance of manoeuvres that they are unable to focus on the finer points of flying—the fear of collision is in many respects a good thing, but if you are thorough and effective in performing the clearing turn prior to flying the manoeuvre, you can take comfort in this and resultantly focus on the flying, having confidence in the knowledge that you have properly cleared the airspace of other traffic and that there is no risk.  Clear airspace, however, can be a temporary and brief state of affairs—perhaps 30 seconds or a minute—as other traffic could move into vicinity airspace, after which another clearing turn must be performed.

4 Standard rate turns are also referred to as “rate-one” turns, and are used in slow flight as there is virtually no “altitude loss” penalty because the angle of bank is so little (consider, for example, the tendency to lose altitude in a steep turn when the lift vector—normally vertical—is deflected substantially into the turn.

5 Most Flight Instructors agree that this is one of the most difficult manoeuvres performed on a flight test, owing primarily for the need for radical pitch and power changes that are associated with the loss of lift.

6 The use of  “normal cruise power” for slow flight recovery can be misleading.  During the practical application of slow flight recovery—recovering from a bounce during a landing attempt, for example—the use of maximum power is often warranted and indeed necessary.

7 The most successful strategy for smooth flap retraction without altitude loss is to ensure the aircraft remains in the slow flight pitch-up attitude when the flaps are retracted—but again, primary reference should be to the altimeter.  What is also important here is your directional control (i.e., keep straight).

Further Readings

Wikipedia

AOPA