PARTIAL PANEL FLYING

Reference, JEPPESEN INSTRUMENT COMMERCIAL MANUAL

PARTIAL PANEL FLYING

If you experience failure of your vacuum-powered gyroscopic instruments in IFR conditions, you will need to transition to flying partial panel, that is, you will be controlling the aircraft primarily with reference to the altimeter, airspeed indicator, turn coordinator, VSI, and magnetic compass. To help prepare you for this possibility, you will practice partial panel flying during your training. In addition, you will be required to demonstrate basic attitude instrument flying on partial panel and be required to fly a partial panel instrument approach during the practical test for your instrument rating.

 

If your gyroscopic attitude indicator and/or heading indicator fails in instrument conditions, you should immediately inform ATC even if control of the aircraft is not an immediate problem. Depending on the conditions, loss of the attitude indicator can be particularly serious, since it may be difficult to comply immediately and accurately with ATC instructions. In many cases, your best option is to divert to a nearby airport with more favorable weather conditions. If you must conduct a partial panel approach in IFR conditions, try to get a radar approach. These approaches, during which ATC provides you horizontal, and, in some cases , vertical course guidance, are covered in detail in Chapter 10, Section A, IFR Emergencies. 

 

STRAIGHT-AND- LEVEL FLIGHT

Since the altimeter normally is your primary pitch instrument, you still have all the information you need to maintain level flight when flying partial panel. However, if your attitude indicator fails, flying straight-and-level is more difficult because the remaining instruments do not provide you with an instantaneous pitch indication. Besides the altimeter, the VSI and the airspeed indicator are your next best instruments for pitch information. Yet, because of lag, these instruments also do not immediately indicate the exact result of a pitch adjustment. Therefore, when flying partial panel, it is even more important to apply gentle, precise control inputs, and patiently watch for the results on your primary instruments. If you inadvertently enter a climb or descent, your first objective is to reestablish level flight, then gently correct back to your intended altitude. If you pay attention to the speed at which the altimeter is moving up or down, it can help you determine the amount of deviation from level flight attitude and the approximate correction you need to make.

 

Without the heading indicator, you must use the magnetic compass and turn coordinator to maintain heading. While doing so, it is important to keep the miniature airplane as level as possible. Even barely visible deviations on the turn coordinator can easily result in heading eπors of 30。 or more within one minute, and the problem is even worse with the older, less precise, turn and slip indicators. Before making adjustments, give the compass time to stabilize in straight-and-level, unaccelerated flight, unless it is obvious that you are significantly off your desired heading. If the compass card bounces or swings, you can average the readings and correct back to your desired heading using timed, standard-rate turns. If you are 10。 away from your desired heading, try a three second standard-rate turn. 

 

TURNS

Use your turn coordinator to establish and maintain partial panel turns. Control of bank is easier than pitch, even with the loss of both the attitude indicator and heading indicator. The turn coordinator, which is your primary instrument for bank, responds quickly enough to adjustments in bank to enable good bank control without the attitude indicator. 

 

Without the support of the attitude indicator, you must use the altimeter, VSI, and airspeed indicator to maintain pitch the same as in straight-and-level flight. But, without the attitude indicator, it is more challenging to accurately compensate for the pitch-change tendencies while maneuvering or during power/airspeed transitions. Gentle control technique, with some knowledge and experience of the required control pressures, helps avoid overcontrolling. Having the airplane properly trimmed before entering a turn is another key factor. Finally, you should increase your scan rate to compensate for the lack of the attitude indicator.

 

COMPASS TURNS

When you use the compass to turn to a northerly heading in the northern hemisphere, remember to roll out before the compass reaches the desired heading. When you turn to a southerly heading, wait until the compass passes the desired heading. As you learned in Section A of this chapter, compass turns should be at standard rate, and the amount of lead or lag approximately equals your latitude. Turning error is small when turning to an easterly or westerly heading; no special correction is needed. When you turn to northwest, northeast, southwest and southeast headings, it may be necessary to use some lead or lag to account for turning error. 

 

While executing compass turns, it is common for instrument students to fixate on the compass during rollout. Remember that until the airplane is stabilized in straight-and level, unaccelerated flight, the indicated heading is not accurate. It is better to concentrate on other instruments to maintain straight-and-level flight before checking the accuracy of your turn.

 

TIMED TURNS

A timed turn is the most accurate way to turn to a specific heading without the heading indicator. In a timed turn, you use the clock instead of the compass card to determine when to roll out. For example, using a standard rate turn (3。 per second), an airplane turns 45。 in 15 seconds. You can still use the magnetic compass to back up the clock, when determining the time to roll out of a turn. 

 

Prior to practicing timed turns, you need to determine the accuracy of the turn coordinator. Establish a standard-rate indication on the instrument for 30 seconds and determine whether the airplane turns 90。. If not, keep repeating the turn, adjusting the bank until you find the turn indication that corresponds to an actual standard-rate turn in each direction. Make a mental note of that indication and use it for standard-rate turns. 

 

Divide the degrees of desired heading change by three degrees per second for a standard rate turn, to get the number of seconds of turn. Start the roll-in when the clock second hand passes a cardinal point, hold the turn at the calibrated standard-rate indication, and begin the roll-out after the computed number of seconds. Do not count the time to roll in and out of the turn, and consider using half-standard-rate turns for small heading changes. 

 

CLIMBS AND DESCENTS

Without the support of the attitude indicator, it is easier to control the transition to a climb if you first slow the airplane to a reasonable climb speed. Although you do not have the benefit of an instantaneous attitude indication, you still have instruments to set climb or descent power. Accurately setting power helps the airplane react predictably and makes it easier to control. However, avoid fixating on the power indicator, especially in partial panel conditions when you need an increased scan rate. Glance at the tachometer or manifold pressure gauge, move the throttle an estimated amount to correct any deviations, and move on with your scan. Check the results of the adjustment in a couple of seconds when your scan returns to the power instrument(s).

 

Use the altimeter, VSI, and airspeed indicator in place of the attitude indicator to make changes in pitch. Because of the lag of these instruments, it is very important to make smooth, gradual control inputs and allow a few moments for the change in pitch to be reflected on these instruments. The rate of movement of the altimeter also gives you indirect pitch information, but requires more interpretation than the VSI.

 

Partial panel bank control during climbing and descending turns is essentially the same as during level turns. Use the compass turn techniques described earlier to determine when to roll out of a turn. Although the most challenging part of partial panel turns is controlling pitch, it is essential you closely monitor your turn coordinator to prevent overbanking which could lead to a diving spiral. Carefully monitor the altimeter, VSI, and airspeed indicator to determine if rolling in or out of the turn has caused undesired deviations.