Operations II: Radar Technique and Windshear

The radar's automatic mode is clever. But the FCTM spends twenty pages teaching manual technique for one reason — the radar is a measuring instrument, not a threat detector: it sees water drops, not turbulence; it paints reflectivity, not danger. Reading the instrument as a threat takes human skill: how to scan tilt, when to reduce gain, how to read shape, why a black hole is scarier than a red blob. The second half of this article is that skill's final exam — windshear: the four-layer defence strategy, eight recognition cues, and the "TOGA + SRS + no config change" memory items.

1. Understand the physics — it is a "water scale," not a "danger gauge"

Per FCTM AS-WXR:

Weather detection is based on the reflectivity of water droplets. The weather echo appears on the ND with a color scale that goes from red (high reflectivity) to green (low reflectivity).

The intensity of the weather echo is associated with the droplet size, composition and quantity (e.g. the reflectivity of a water particle is five times more than an ice particle of the same size). The flight crew must be aware that the weather radar does not detect weather that has small droplets (e.g. clouds or fog), or that does not have droplets (e.g. clear air turbulence).

"Water is five times the ice" is the article's key: a cell top is all ice crystals, so the "top" the radar sees is always lower than the real cloud top. Per FCTM AS-WXR:

‐ The radar top is not the visible top of the storm cell ‐ The storm cell and associated turbulence extend significantly above the radar top.

"Clear on the display" ≠ "clear over the top" — the first commandment of overflight decisions.

2. Tilt technique — bite the "wettest layer"

Per FCTM AS-WXR:

The tilt refers to the angle between the antenna beam centerline and the horizon. The radar uses data from the IRS to stabilize its antenna. Therefore, the antenna tilt is independent of the aircraft pitch and bank angle.

(Climb at 3° nose-up and the beam does not follow — it knows the inertial horizon.) The scan discipline. Per FCTM AS-WXR:

The flight crew should regularly scan the area ahead of the aircraft, at several ND ranges. In order to identify the strongest weather returns, the flight crew should tilt the weather radar antenna up and down.

To obtain a correct display of a storm cell, the flight crew must use the tilt knob to point the weather radar beam to the most reflective part of the storm cell. A correct tilt setting prevents the overscanning of the storm cell.

Overscanning is a high-altitude killer. Per FCTM AS-WXR:

At high altitude, a storm cell may contain ice particles that have low reflectivity. If the tilt setting is not correct, the ND may display only the upper (less reflective) part of a storm cell (overscanning). As a result, the flight crew may underestimate or not detect a storm cell.

The beam sweeps the ice "cap" and the wet core slips below it — a small green blob, a big red cell underneath. The folk cure is one line. Per FCTM AS-WXR:

Common practice is to ensure that the ground return is at the top of the ND screen.

Geometrically: the beam's lower edge grazes the ground at the far end of the selected range — the whole route's low-to-mid altitude is in the beam, and the wet core cannot escape. Range division. Per FCTM AS-WXR:

‐ 160 NM on the PM ND ‐ 80 NM on the PF ND.

Over water there is no ground return to top the screen; use an initial value from a table. Per FCTM AS-WXR:

For flights above the water, there are no ground returns. Therefore, the flight crew can use any of the following tilt settings at cruise altitude as an initial value before adjustment: ‐ Approximately -6 ° for an ND range of 40 NM, or ‐ Approximately -2 ° for an ND range of 80 NM, or ‐ Approximately -1 ° for an ND range of 160 NM, or ‐ Approximately -1 ° for an ND range of 320 NM.

Cannot tell ground from weather? Move the tilt. Per FCTM AS-WXR:

It is difficult to identify the difference between weather returns and ground returns: A change in the tilt setting causes the shape and color of ground returns to rapidly change. These ground returns eventually disappear. This is not the case for weather returns.

This is a Multiscan automatic radar, so the corresponding FCTM discipline is: AUTO normally, switch to MAN to analyse a cell with the technique above, then return to AUTO (Use manual tilt for storm cell analysis, then set tilt back to AUTO.) — forget to return and you have dismissed hazard prediction and PAC.

3. The top-estimate formula and gain analysis — two "surveyor's tools"

Top estimate: scan the cell until it just disappears from the ND and record the tilt and range. Per FCTM AS-WXR:

h(ft) is the difference between the radar top altitude and the aircraft altitude. d(NM) is the distance between the aircraft and the storm cell. Tilt(°) is the tilt setting for which the storm cell image disappears from the ND.

Example: a weather return that disappears from the ND at 40 NM with a tilt setting of 1 ° down, indicates that the top of the storm cell is 4 000 ft below the aircraft altitude.

The formula (from the example, a 1° beam offset ≈ 100 ft per NM): h ≈ d × tilt × 100. Disappearing on up-tilt = the top above you by that much; on down-tilt = below. Layered with §1's commandment, what you compute is the radar top — the real turbulence top is higher still (the source of the 5000 ft margin, §5). Gain can also help: The flight crew can increase the gain in order to obtain a more visible display of the top of the storm cell. Reduce gain to find the core. Per FCTM AS-WXR:

When operating in heavy rain, the weather radar picture can be saturated. In this case, manually reduce the gain will help the flight crew to identify the areas of heaviest rainfall, that are usually associated with active storm cells.

After a storm cell analysis, the flight crew must set the GAIN knob back to AUTO/CAL.

(Under manual gain the colours are no longer calibrated — forget to return and everyone downstream is fooled. The ND's first line MAN GAIN is the reminder.)

4. Four reading rules — shape, contrast, black hole, wedge

Colour lies. Per FCTM AS-WXR:

Particle reflectivity of a storm cell is independent of the potential weather hazard in the storm cell.

A high-humidity coastal thermal cell "all red" may not be fierce; an equatorial inland dry-convection cell reflects weakly but may be extremely fierce. Per FCTM AS-WXR:

The flight crew must not underestimate a storm cell with a high vertical expansion, even if the weather return is low.

Shape is the truth. Per FCTM AS-WXR:

The flight crew should carefully observe shapes, more than colors, in order to detect adverse weather conditions. Areas of different colors that are near to one another usually indicate zones of severe turbulence. Some shapes are good indicators of severe hail and signify strong vertical drafts. Shapes that change quickly, whatever form they take, also indicate high weather activity.

The black-hole law (attenuation, the human version of the PAC yellow arc). Per FCTM AS-WXR:

In areas of heavy precipitation, an important part of the weather radar signal is reflected by the frontal part of the precipitation due to its strong reflectivity. Therefore, the area behind the precipitation returns low signals, that appears as green or black areas (storm shadows).

On a weather radar display, the flight crew should always consider a black hole behind a red area as a potentially very active zone.

The blind-alley effect. Per FCTM AS-WXR:

a course change that may appear safe with a short ND range, may be blocked when observed with a higher ND range.

Weave into a gap between two returns on short range, and on long range the gap's far end is a wall — a course-change decision always reads both short and long range (the other meaning of the 160/80 division). The last oddity — radar interference (spoking). Per FCTM AS-WXR:

The radar return will appear as a single wedge that extends out along the ND toward the source of interference.

Not weather, no damage to the machine, self-healing out of the scan zone (This interference does not damage the radar system) — recognise it so you do not deviate around a false spike.

5. Convective operations — four numbers, one mindset

Three detection reminders. Per FCTM AS-WXR:

‐ Always consider that a convective cloud may be dangerous, even if the weather echo is weak. Remember that the weather radar detects only water droplets ‐ Frequent lightning may indicate an area with high probability of severe turbulence ‐ Remember that the TURB function detects areas of wet turbulence only

Decision timing. Per FCTM AS-WXR:

Initiate your avoidance maneuver as early as possible. As the aircraft gets nearer to the convective weather zone, the information from the weather radar often becomes partial. Consider a minimum distance of 40 NM from the convective cloud to make the decision for avoidance maneuver.

The mindset: first draw an "area of greatest threat" from the strongest echoes plus meteorological knowledge — avoid the area, not the pixels; the hazard red dots yield to the echo itself. Per FCTM AS-WXR:

The weather hazard prediction function (if installed) indicates zones with a high probability of weather hazards (hail or lightning). Avoidance of the detected weather always has priority over avoidance of the weather hazards.

The mode of avoidance. Per FCTM AS-WXR:

If possible, perform lateral avoidance instead of vertical avoidance. Vertical avoidance is in general not recommended, particularly at high altitude, due to the reduction of buffet and performance margins. In addition, some convective clouds may have a significant and unpredictable build-up speed.

If possible, deviate upwind instead of downwind. Usually, there is less turbulence and hail upwind of a convective cloud

Laterally clear the "area of greatest threat" by at least 20 NM (more for dynamic cells); if you must overfly, keep 5000 ft vertical margin above it; and do not go below a cell even visually. Per FCTM AS-WXR:

Avoid flying below a convective cloud, even in visual conditions, due to possible severe turbulence, windshear, microbursts, lightning strikes and hail.

6. Ice crystals — the opponent the radar can barely see

Where it hides. Per FCTM AS-WXR:

Areas of ice crystals are usually next to, or above the core of convective clouds that have high-intensity precipitation. However, areas of ice crystals may sometimes even be several nautical miles away from the core of the associated convective cloud.

Why it is hard to defend against. Per FCTM AS-WXR:

Ice crystals are difficult to detect with the weather radar, because their reflectivity is very low due to both their small size and solid state.

This is because ice crystals bounce off cold aircraft surfaces. This is why even the ice detection system does not detect ice crystals, because ice crystals do not build up on ice detectors and visual ice indicators.

(It melts and re-freezes only on hot surfaces — the engine core, heated probes — striking exactly the vital parts.) Cockpit cues: "rain that should not exist" on the windshield at low temperature, plus a hissing sound. Per FCTM AS-WXR:

‐ Small accumulation of ice particles on wipers ‐ Smell of ozone or Saint Elmo’s fire ‐ Aircraft TAT indication that remains near 0 °C (due to freezing of the TAT probe) ‐ Light to moderate turbulence in IMC at high altitude

The radar face — "black above, red below, downwind." Per FCTM AS-WXR:

‐ No significant radar echo at high aircraft altitude, combined with: • High-intensity precipitation that appears below the aircraft, or • Aircraft position downwind of a very active convective cloud.

Handling = the same as convective avoidance (lateral, upwind, margins) + a special note to scan downward (strong echo underfoot = ice crystals possibly above you); if you do enter and it causes engine/probe misbehaviour, follow the ECAM and QRH (ice crystals are on the unreliable-airspeed cause list).

7. Windshear — the full four-layer defence strategy

Memorise the enemy's portrait first (the FCTM's energy trap). Per FCTM PR-NP-SP-10-10-2:

An aircraft that approaches a microburst will first encounter a strong headwind. This can result in an increase in the indicated airspeed. This may cause the aircraft to fly above the intended flight path and/or accelerate. With a fixed speed on approach, the flight crew’s reaction may be to reduce power. This will cause the aircraft to fly with reduced energy through the downburst. The wind will then become a tailwind. The indicated airspeed and lift will drop and the downburst may be sufficiently strong to force the aircraft to lose a significant amount of altitude. The degraded performance, combined with a tailwind encounter, may cause the aircraft to stall.

The headwind lures you to give up energy, the tailwind comes to collect — every defence is built around this trap. The best handling is always layer zero. Per FCTM PR-NP-SP-10-10-2:

If a windshear encounter is likely, the takeoff or landing should be delayed until the conditions improve, e.g. until a thunderstorm has moved away from the airport.

Eight recognition cues (the human detector's calibration): IAS variation over 15 kt, ground-speed variation, ND wind jumps, vertical-speed excursion of 500 ft/min, pitch excursion of 5°, glideslope deviation of 1 dot, heading variation of 10°, unusual A/THR activity. The four-layer strategy (aware–inform–warn–escape): aware = PWS (Doppler on raindrops, seen before entry); inform = FPV + GS mini. Per FCTM PR-NP-SP-10-10-2:

Approach speed variations and lateral FPV displacement reflect horizontal wind gradient. Vertical FPV displacement reflects the vertical air mass movement.

(Read the bird with the speed tape: a sudden target-speed jump = GS mini smelling a headwind; the bird dropping = the air mass pulling you down.) Warn = the order of two aural warnings. Per FCTM PR-NP-SP-10-10-2:

This warning attracts the PF’s eyes to the speed scale, and requests rapid thrust adjustment. In windshear conditions, it is the first warning to appear, before the activation of the alpha floor protection.

How subtle the trigger is, the table shows. Per FCTM PR-NP-SP-10-10-2:

-1 kt/second -3 ° VLS -7 kt

-1 kt/second -4 ° VLS -1 kt

(It looks not at speed but at the energy trend of speed + acceleration + flight-path angle — the steeper the path, the earlier it calls.) The reactive «WINDSHEAR» ×3 is the declaration "already inside." Escape tools = a trio: alpha floor (A/THR auto-TOGA, FMA A.FLOOR → TOGA LK, cleared only by turning A/THR off), the SRS pitch guidance, and the high-AOA protection. Per FCTM PR-NP-SP-10-10-2:

The high AOA protection enables the PF to safely pull full aft stick, if needed, in order to follow the SRS pitch order, or to rapidly counteract a down movement. This provides maximum lift and minimum drag, by automatically retracting the speed brakes, if they are extended.

8. Phase-by-phase decisions and the memory items

Establish the PWS trust level first: some airports have known spurious-alert records — a PWS warning may be disregarded under three conditions (no hazard confirmed, no other windshear signs, reactive system operative); but. Per FCTM PR-NP-SP-10-10-2:

However, the flight crew must rely on all reactive windshear (i.e. WINDSHEAR) alerts.

(Prediction is suspect; reality brooks no doubt.) The take-off roll decision matrix. Per FCTM PR-NP-SP-10-10-2:

If a predictive windshear warning is triggered during the takeoff roll, the Captain must reject takeoff.

If a predictive windshear caution is triggered during the takeoff roll, it is the decision of the Captain according to the Captain's situation assessment to either: ‐ Continue with takeoff considering TOGA, or ‐ Reject takeoff.

Reactive recognition (the «WINDSHEAR» aural is inhibited during the roll — it is on the human). Per FCOM PRO-ABN-SURV:

If there are significant variations in airspeed, and in airspeed trend below the indicated V1, reject the takeoff.

If windshear occurs during the takeoff roll, the aircraft may reach V1 later (or sooner) than expected. The flight crew should ensure that there is sufficient runway remaining to stop the aircraft, if necessary.

After V1 / airborne (reactive or crew-detected) = memory item: thrust levers TOGA (confirm if already), rotate at VR, follow SRS (full backstick if needed), keep the AP engaged (it releases itself only above α-prot). Per FCOM PRO-ABN-SURV:

If the FD bars are not displayed, move toward an initial pitch attitude of 17.5 °. Then, if necessary, to prevent a loss of altitude, increase the pitch attitude.

DO NOT CHANGE CONFIGURATION (SLATS/FLAPS, GEAR) UNTIL OUT OF WINDSHEAR.

(Why not even retract the gear? The FCTM gives the engineering answer: operating the landing gear doors causes additional drag — retracting opens the doors first, so drag rises before it falls, and the most energy-starved seconds cannot afford that up-front cost.) And out of it. Per FCOM PRO-ABN-SURV:

WHEN OUT OF WINDSHEAR, SMOOTHLY RECOVER NORMAL CLIMB.

On approach: a PWS caution / suspected windshear — delay or divert first; if determined to continue, five equipment items: assess severity with the radar, choose the best runway, land FLAPS 3 (optimising go-around gradient), use managed speed (the point is GS mini), and for a strong/gusty crosswind (> 20 kt) VAPP at least VLS+5 (crew discretion to +15); «GO AROUND WINDSHEAR AHEAD» → TOGA go-around; reactive on approach = unconditional TOGA go-around, the same "SRS + no config change + PM calls wind" discipline, with the PM's role stated. Per FCTM PR-NP-SP-10-10-2:

‐ The PM should call out the wind variations from the ND and V/S and, when clear of the windshear, report the encounter to the ATC.

Key numbers

Self-test

[!note]- Q1. FL360 level, a green return 60 NM ahead disappears only at +2° up-tilt — where is its top? Passable? (formula + radar-top commandment) h ≈ 60 × 2 × 100 = 12000 ft above you (up-tilt). Even if the display clears, the radar top is not the cloud top and turbulence extends above — do not overfly on the display alone.

[!note]- Q2. All-red saturation, which knob, how, and what to watch? The GAIN knob, reduce it: the wettest core fades last = the active cell. Return to AUTO/CAL after.

[!note]- Q3. "Clean black behind a red cell" — first reading? Relation to the PAC yellow arc? Treat it as a potentially very active zone (attenuation shadow). The PAC yellow arc is the automatic version of the same thing.

[!note]- Q4. Why deviate upwind of convection, and what two things hide below? Less turbulence and hail upwind (the anvil and hail are swept downwind). Below hide severe turbulence, windshear/microbursts, lightning and hail.

[!note]- Q5. Why are both the ice detector and radar blind to ice crystals? Give three cockpit cues and the radar face. Crystals are small, solid, low-reflectivity and bounce off cold surfaces (no build-up on detectors). Cues: windshield "rain" + hiss, wiper ice, TAT frozen ~0 °C. Radar face: no echo at your altitude with strong precip below / downwind of an active cell.

[!note]- Q6. Take-off roll at 90 kt, «MONITOR RADAR DISPLAY» — who decides, on what? And «WINDSHEAR AHEAD»? Caution: the captain decides (continue with TOGA or reject) on situation assessment. Warning: the captain must reject.

[!note]- Q7. In the escape, why not retract the gear, and when does the AP release itself? Retracting opens the doors first (drag up before down) — unaffordable when energy-starved. The AP releases itself above α-prot.

Key takeaways

References

• FCTM AS-WXR — radar physics, tilt technique, gain, four reading rules, convective operations, ice crystals.
• FCTM PR-NP-SP-10-10-2 — windshear phenomenon, eight cues, four-layer strategy, SPEED table, phase decisions.
• FCOM PRO-ABN-SURV — reactive windshear memory item.

Independent study material, not an Airbus publication and not endorsed by the manufacturer. Always defer to the current operator FCOM, FCTM, and QRH for operational use.