Learn › Maneuvers › Instrument Straight-and-Level Flight

Instrument Straight-and-Level Flight

The horizon is a reference you borrow from outside the airplane, and some days it is not there. This maneuver is not how you keep going without it — it is how you stay upright long enough to turn around and get back to where it is.

Basic Instrument Maneuvers — FI.XI.A

Why you learn it

Every private pilot certificate contains three hours of flight training on the control and maneuvering of an airplane solely by reference to instruments, required by 14 CFR 61.109(a)(3), and the FAA is plain about what those hours are for. They are an escape, not a capability. A pilot who is not instrument rated and not current has no business in cloud, and being in cloud anyway is an emergency. Three hours is enough to keep an airplane from getting away from you; it is nowhere near enough to make cloud a place you can operate.

So the first action on losing visual reference is not to settle in and fly on the gauges indefinitely. It is a 180-degree turn, shallow and standard rate, back toward the conditions you were in a minute ago, because those are the only conditions you know for certain are flyable. Straight-and-level is what you hold before that turn, what you return to when you roll out, and what you keep holding while you sort out terrain, fuel and who to talk to.

The horizon does not usually vanish all at once. It goes three ways, and all three are things you can see coming. Night VFR near clouds, where the layer you entered was invisible until you were inside it. Deteriorating weather that closes in slower than you were willing to turn around. And fog, forming underneath you as the temperature settles onto the dewpoint — which is why a small and shrinking temperature-dewpoint spread on the METAR is a warning and not a detail.

What happens after that is not really a flying problem. With no outside reference your inner ear hands you an attitude, confidently and wrongly, and the sensation is strong enough that pilots have flown serviceable airplanes into the ground while disbelieving instruments that never failed. Decide it on the ground: you believe the panel, you start scanning the moment you lose visual reference rather than waiting to see whether the cloud thins out, and you begin the turn back rather than pressing on to see what is on the other side.

Everything else you will ever do on the gauges — climbs, descents, turns to a heading, a recovery from an unusual attitude — is assembled out of this one, and none of it works if you cannot hold a heading and an altitude with nothing to look at but the panel.

What you are flying on

Three systems feed the panel. The pitot-static instruments — airspeed indicator, altimeter, vertical speed indicator — work from pressure. The gyroscopic instruments — attitude indicator, heading indicator, turn coordinator — work from a spinning mass, or from the solid-state sensors doing the same job in a modern panel. And the magnetic compass, which needs no power from the airplane at all, which is why it is still there after everything else has quit. The inclinometer beside the turn coordinator belongs to none of the three: it is a ball in a fluid-filled tube, showing slip and skid because gravity and inertia move it, and nothing is spinning inside it.

The attitude indicator is the only instrument that shows you pitch and bank directly. Every other one reports a result, and reports it slightly late.

A glass panel arranges the same information around that idea. The attitude display fills the middle. The airspeed tape sits on the left, the altimeter tape on the right with the vertical speed scale beside it, the horizontal situation indicator underneath, and the turn rate scale just above the HSI. Power lives on the engine display, usually on the multifunction screen — worth noticing, because power is half of what makes level flight level and it is the one item not in front of you.

The tapes also draw trend vectors, a bar predicting where the number will be a few seconds from now. Trends are useful and they are not measurements. Fly from what the altitude and airspeed actually are.

The scan

Scan out from the attitude indicator and back to it — hub and spoke. Read one instrument, return to the attitude indicator, read the next one, return again. This is the selected radial scan, and it is one of several patterns the Instrument Flying Handbook describes rather than the only sanctioned one. What the workable patterns share is where they spend their time: the attitude indicator is where you make the correction, and the other instruments exist to tell you whether the correction was the right size, so the attitude indicator is the one you come back to most.

Underneath the scan sit two methods, and you will use both. Control and performance says that attitude plus power gives performance: set the pitch and bank you want, set the power the POH calls for, and the airspeed, altitude and heading follow. Primary and supporting says that in any given flight condition one instrument gives the most direct information about each of pitch, bank and power. Straight and level at a constant airspeed, the altimeter is primary for pitch, the heading indicator is primary for bank, and the airspeed indicator is primary for power, with the vertical speed indicator and the rest supporting them. Either way, chasing the altimeter with the yoke works the problem backwards — the altimeter tells you what to change, the attitude indicator is where you change it.

Flying it

Set the miniature airplane on the attitude indicator to your own seated eye level before you need it; it is a reference you adjust, not a fixed truth. Then establish an approximate level attitude, wings level and the nose about where level flight puts it in that airplane at that weight, set the power the POH gives for the cruise you want, and let it stabilize. There is no single pitch picture for level flight. It moves with airplane, weight and power setting, so you find the right one by refining against the altimeter rather than by memorizing a sight picture. Once the altitude is holding, trim until you are holding nothing.

Trim is not a comfort item here. Every pound of pressure you are holding is attention spent on your hands instead of the scan, and the airplane will drift the instant you look away.

Corrections are small and deliberate. If the altitude is off a little, change pitch by an amount you can barely see on the attitude indicator, let it settle, then re-trim. If it is off by more, or the airspeed has decayed, the answer is power as well as pitch. For heading, check that the wings are level and the ball is centered, then correct with a shallow bank — a small heading error does not need a steep one — hold it, and roll out on the number.

Level flight is not one attitude you find once. Fuel burns off and the air changes, so the picture drifts as the flight goes on. Holding it is a continuous sequence of very small corrections, which is why the scan never stops.

What goes wrong

Nearly all of it is scan failure, in three flavors. Fixation — you stare at the altimeter willing it back to the number while the heading walks off. Emphasis — you fly the trend vector instead of the actual rate, or trust one instrument and ignore what the others say about it. Omission — the engine indications never get looked at, so a power problem shows up first as an airspeed you cannot explain.

The other reliable failure is over-controlling. A large input produces a large correction, which produces a large correction the other way, and the altitude oscillates wider each time. Small inputs, then wait.

When the panel quits

Know what a failure looks like before it happens. On a glass panel a failed sensor or data source generally shows as a red X over the affected display. What the panel does next is installation-specific: some avionics offer a reversionary mode that puts the essential instruments back on the remaining screen, some revert automatically, and some installations have no reversion at all. The AFM supplement for the avionics in your airplane is the only authority on which one you have — read it, and find the switch on the ground rather than in cloud.

On a conventional panel the equivalent skill is partial panel, and this is where primary and supporting earns its keep. With the attitude indicator gone, the supporting instruments become the primary ones: fly pitch on the altimeter, airspeed and vertical speed indicator, and bank on the turn coordinator and the magnetic compass, remembering that the compass only tells the truth in steady, level, unaccelerated flight.

If the autopilot is working and you are saturated, use it. Know how it disengages and what mode it is in, so you are not surprised twice. And use the controller: unable VFR, request vectors is a complete transmission, and the sooner it is said, the more options are left. If you are not instrument rated and you are in cloud, say that it is an emergency as well. Declaring buys you priority, terrain and traffic separation and somebody else carrying part of the workload, and whatever paperwork occasionally follows is a trade worth making.

The standards

The task is PA.VIII.A, Private Pilot ACS, Area of Operation VIII, Basic Instrument Maneuvers, Task A. The tolerances are altitude within 200 feet, heading within 20 degrees, and airspeed within 10 knots. They are deliberately generous, because what is being examined is not precision instrument flying but whether a VFR pilot can keep an airplane controlled and pointed somewhere useful while the eyes do unfamiliar work. The instrument rating tightens the same numbers to 100 feet and 10 degrees. If you cannot hold the private tolerances in smooth air under a view-limiting device, you will not hold anything in the weather that made you need this.

Where you meet it next

On the checkride it is the first task of the basic instrument maneuvers block, flown under a view-limiting device, and the rest of that block is this same scan doing more work: constant airspeed climbs and descents, turns to headings, and recovery from unusual flight attitudes, which is what straight-and-level looks like once it has been allowed to fail. They are asked for one after another under the hood, so what is really being tested across all of them is the cross-check.

It is also the visual maneuver with the window taken away. The trim technique and the small-correction habit are the ones from straight-and-level flight, and they transfer back and forth intact. Further out it is the ancestor of everything on the instrument rating, where holding altitude and heading while reading a chart, talking on the radio and briefing an approach is the real skill being tested. The ground school library covers the weather that puts you here in the first place.