How to read a primary flight display: the six things a pilot looks at
A beginner's guide to the PFD: attitude, speed tape, altitude, vertical speed, heading and the mode strip, in the order a pilot actually looks at them.
The first time you sit in the left seat of an airliner cockpit, it looks like far too much at once. It is not, and the reason is that almost everything you need to fly is on a single screen right in front of you: the primary flight display, the PFD. Learn to read that one screen and the rest of the panel becomes scenery you can study later.
I make Open Flight World, and this is the guide I wish I had had on my first flight in a big cockpit. Six things, in the order a pilot looks at them.
One screen instead of six dials
Before glass cockpits, this same information lived in six round instruments arranged in two rows of three. The PFD drew those six on one screen, in the same places: the horizon in the middle, the speed on the left, the altitude on the right, the vertical speed beside the altitude, the compass underneath and a strip across the top telling you what the automation is doing.
That layout is nearly the same in every modern airliner, which is the best news in this article: once you can read the PFD of one aircraft, you can read the next one. The numbers change. Where they live does not.
The order matters more than the list
A pilot does not read the PFD from left to right like a page. The scan starts in the middle, goes out to one item, and comes straight back to the middle: attitude, speed, attitude, altitude, attitude, vertical speed, attitude, heading. Out and back, a few times a minute.
The reason is simple. The attitude is the only item that tells you what the aircraft is doing right now. All the others tell you what it has already done. If the nose is where you want it and the wings are level, the speed and the altitude will behave; if you stare at the altitude while the nose creeps up, you will find out about it too late.
1. Attitude: the horizon in the middle
The big blue and brown display in the centre is the artificial horizon. Blue is sky, brown is ground, and the line between them is the real horizon, drawn even when cloud or night hides it.
- The little wings or triangle in the middle are your aircraft. Where they sit against the horizon line is your pitch.
- The ladder of short lines above and below the horizon measures that pitch in degrees. On an airliner, a takeoff is roughly 12 to 15 degrees of nose up, a normal climb a bit less, and level cruise sits within a couple of degrees of the horizon.
- The arc at the top, with its marks at 10, 20, 30 and 45 degrees, is the bank. A normal turn is about 25 to 30 degrees of bank, and it feels like a lot the first time.
One glance here answers the only question that really matters: is the nose where I left it, and are the wings level?
2. Speed: the tape on the left
The moving ribbon on the left is the airspeed, in knots. Your current speed is the number in the box in the middle of the tape, and the tape slides down as you speed up.
Two things on it are worth more than the number itself:
- The trend arrow. A small arrow that stretches up or down from the box and points at the speed you will have in about ten seconds if nothing changes. It is how you notice that you are slowing down long before the figure looks wrong.
- The limits. A red and black band at the top of the tape marks the fastest you may fly, and markings at the bottom show the slowest for your present flaps and weight. Your job on an approach is to keep the box away from both ends.
Speed is the item beginners neglect, and it is the one that bites. In a Cessna 172 the whole landing hangs on about 65 knots on final; an airliner has its own numbers, but the habit is the same.
3. Altitude: the tape on the right
The ribbon on the right is the altitude in feet, read the same way: the number in the box is where you are now. Beside it you will usually find the altitude you have asked the autopilot for, drawn as a marker on the tape so you can see the gap closing.
At the bottom of the tape sits the pressure setting the altimeter is using, which is why two aircraft at the same height can read differently if one of them has the wrong figure. The standard setting, used by everyone up high, is 1013 hPa or 29.92 inches.
Altitude is a slow instrument. It tells you where you have arrived, not where you are going. For that you need the next one.
4. Vertical speed: the needle beside the altitude
Tucked against the altitude tape is the vertical speed, in feet per minute: up is a climb, down is a descent. It reacts quickly, which makes it useful and also makes it a trap, because it wanders with every small bump.
The figures worth remembering:
| Vertical speed | What it means |
|---|---|
| 1,500 to 2,500 ft/min | A normal airliner climb after takeoff |
| about 700 ft/min | A 3 degree approach at 140 knots of groundspeed |
| about 325 ft/min | The same 3 degree path at 65 knots, in a Cessna |
| more than 1,000 ft/min, low down | Too fast a descent on an approach. Fix it now |
There is a handy rule behind that table: on a 3 degree path, your rate of descent in feet per minute is roughly five times your groundspeed in knots.
And the discipline: set the attitude, then let the vertical speed settle. Never chase the needle with the controls, or you will spend the flight rocking up and down.
5. Heading: the compass at the bottom
Under the horizon is the compass, either a tape or the top half of a rose. The number under the index at the top is the direction the nose is pointing, in degrees: 360 is north, 090 east, 180 south, 270 west. A runway's number is simply its heading with the last digit dropped, so runway 09 points about 090.
Many displays also show your track, the direction you are actually travelling over the ground. With a crosswind the two differ, and the gap between them is the drift the wind is giving you. In Open Flight World the live wind blows along your departure runway, so it is mostly a headwind and the drift stays small, which is a kind way to meet the idea.
6. The strip across the top: who is flying
The band of green and white words along the top of the PFD is the mode strip, the flight mode annunciator. It tells you, in a few short labels, what the thrust is doing, what the autopilot is doing with the wings, what it is doing with the nose, and whether it is engaged at all.
It is the last item of the scan and the first cause of confusion in a real cockpit. The rule the airlines teach is worth borrowing: if the strip does not say what you expected, the aircraft is not doing what you expected. Read it after every change you make, and before you sit back and admire the view.
The six at a glance
| Where | What it is | What you ask it |
|---|---|---|
| Middle | Attitude | Is the nose where I left it, are the wings level? |
| Left | Speed tape | Am I fast, slow, or heading that way? |
| Right | Altitude | Where am I, how far from where I asked for? |
| Beside the altitude | Vertical speed | Up or down, and how quickly? |
| Bottom | Heading | Where is the nose pointing, and where am I going? |
| Top | Mode strip | Who is flying, and in what mode? |
Practising the scan in Open Flight World
Reading about a PFD is like reading about swimming. Open the simulator and try the scan with the aircraft moving.
- Start in the Cessna, free. The Cessna 172 at London City is free, in photorealistic 3D, with no account, no ads and no time limit. The panel is simpler than an airliner's, and the four items in the middle of the scan are the same four. Then the Airbus A320neo, the Boeing 787-9, the ATR 72-600 or the Challenger 350 give you the airliner version; those are among the paid aircraft, each unlocked once and kept, or opened with All Access. The details are on the pricing page.
- Sit in the cockpit. C cycles the camera, so you can put yourself behind the panel instead of behind the tail, and Enter centres the view.
- Pause and read. P stops the flight. Freeze a climb, take thirty seconds over the six items, and let it run again. V replays the last minute if something happened faster than you could read it.
- Watch the autopilot fly a good approach. Press A and let it fly the 3 degree path to the runway and land. It is the cleanest demonstration you will get of a stable approach seen through the instruments: speed steady, vertical speed around 700, heading on the runway, altitude unwinding at an even rate.
- Then fly it yourself. Choose the Landing start position, keep the coach on in the simple mode of the controls guide (F1) so it calls the speeds while you learn where to look, and press R to go round again. H shows or hides the HUD when you want nothing but the cockpit.
If you have not taken off yet, start with how to take off in a flight simulator, then how to land a Cessna 172 and how to use the autopilot. The keys all live in the controls cheat sheet.
The four mistakes everyone makes
- Fixating on one item. Thirty seconds staring at the altitude is thirty seconds of not knowing where the nose is. Always come back to the middle.
- Flying the numbers instead of the attitude. Set a pitch, wait, then read the result. The instruments answer the attitude, not the other way round.
- Chasing the vertical speed. It is the twitchiest thing on the screen. Correct gently, and only if it stays wrong.
- Ignoring the strip at the top. Most of the puzzling moments in an airliner cockpit, simulated or real, are explained in those few words.
Get the six into a loop and the cockpit stops being a wall of numbers. It becomes one picture, and you will find yourself reading it with the same glance you give the speedometer in a car.
Frequently asked questions
What does PFD mean?
Primary flight display. It is the screen in front of each pilot that gathers the six basic flight instruments into one picture: attitude, airspeed, altitude, vertical speed, heading and the strip that says what the autopilot is doing.
In what order should I read a PFD?
From the middle outwards and back again. Attitude first, then one item, then back to the attitude: attitude, speed, attitude, altitude, attitude, vertical speed, attitude, heading. The attitude is the only instrument that tells you what the aircraft is doing right now.
What is the little arrow on the speed tape?
The speed trend. It points to the speed you will have in about ten seconds if nothing changes, so it tells you whether you are accelerating or slowing down before the number moves much.
Can I practise reading a PFD in a browser?
Yes. In Open Flight World every aircraft is built with its own 3D cockpit and instruments, so you can sit in the cockpit view, pause the flight with P and read the screen at your own pace. The Cessna 172 at London City is free; the airliners are among the paid aircraft.
Do I need to understand the PFD before my first flight?
No. You can fly with the coach calling out the speeds and look at the screen afterwards. But the six items on this page are what turn a wall of numbers into a picture you can read in one glance.
