ICAO Technical Problem Vocabulary – Aircraft Systems, Malfunctions & Failures

ICAO Technical Problem Vocabulary

Precise technical descriptions of onboard mechanical, electrical, and hydraulic degradations are central to the ICAO Language Proficiency Assessment (Doc 9835 and Annex 1). During oral examinations, language raters evaluate whether flight crews and Air Traffic Control Officers (ATCOs) can describe system malfunctions in plain, unambiguous English when standard radiotelephony phraseology does not fully convey the operational scope of an abnormality.

To achieve ICAO Level 4 (Operational), Level 5 (Extended), or Level 6 (Expert), candidates must move beyond vague terminology like "the plane is broken" or "the computer failed." This guide organizes key technical vocabulary across five core aircraft system domains: Hydraulic & Pneumatic Systems, Electrical Power Generation & Distribution, Avionics & Automated Flight Control Systems (AFCS), Flight Control Surfaces & Actuators, and Braking & Landing Gear Malfunctions.

ICAO Technical Problem Lexicon Overview

differentiate hydraulic pressure losses, reservoir depletion, and pneumatic bleed air duct ruptures
understand electrical anomalies: generator trips, essential bus shedding, inverter faults, and APU failures
articulate avionics failures: uncommanded autopilot disengagement, pitot-static blockages, and TCAS/EGPWS warnings
describe mechanical control surface defects: stuck ailerons, runaway stabilizer trim, and flap/slat asymmetry
master landing gear and braking issues: anti-skid faults, hot brakes, gear pin omissions, and tire blowouts
practice model spoken responses for ICAO Speaking Part 2 picture descriptions, Part 3 role-plays, and Part 4 discussions

Step 1: Hydraulic & Pneumatic System Malfunctions

Heavy transport aircraft rely on multi-redundant hydraulic and bleed-air systems for flight controls, landing gear extension, and cabin conditioning. Use accurate mechanical terms to describe system degradation:

Technical Term	System Nature & Operational Mechanism	Model Example Sentence
Hydraulic Reservoir Depletion	Total or partial loss of hydraulic fluid volume within a reservoir caused by lines fractured under vibration or pump seal degradation.	"The crew declared an urgency state after identifying complete hydraulic reservoir depletion* in the left system."*
Bleed Air Duct Leak / Rupture	Escape of high-pressure, superheated air extracted from engine compressor stages, posing overheat risks to surrounding wing and fuselage structures.	"A bleed air duct leak* triggered an automated isolation valve closure, reducing air conditioning pack efficiency."*
Ram Air Turbine (RAT) Deployment	Automatic or manual release of an external slipstream-driven turbine to supply emergency hydraulic pressure or electrical power following dual-engine failure.	"Following total electrical failure, the RAT deployed* successfully to power primary flight control actuators."*
Pressure Drop / Fluctuations	Unsteady or sub-nominal hydraulic system pressure, indicating pump cavitations, internal check valve leakage, or filter clogging.	"The pilot monitored erratic pressure fluctuations* before manually isolating the center hydraulic circuit."*

Step 2: Electrical Power Generation & Distribution Anomalies

Electrical abnormalities can rapidly degrade flight instruments, radios, and cockpit automation. Differentiate electrical components and failure types:

Electrical Anomaly	Physical Manifestation & Cockpit Indication	Operational Resolution
Integrated Drive Generator (IDG) Trip	Mechanical disconnection or electrical tripping of an engine-driven generator due to internal oil over-temperature or over-torque.	Start Auxiliary Power Unit (APU) generator or cross-tie electrical buses to redistribute alternating current.
Automatic Bus Tie / Load Shedding	The automatic de-energizing of non-essential electrical systems (e.g., galley power, passenger entertainment) to preserve battery power for essential flight instruments.	Acknowledge ECAM/EICAS master caution and configure cockpit for single-generator flight profile.
Static Inverter Failure	Malfunction of the solid-state device converting Direct Current (DC) battery power into Alternating Current (AC) for standby avionics.	Monitor standby attitude indicators and confirm battery charging current via maintenance synoptic pages.
Thermal Runaway (Lithium-Ion Battery)	An uncontrollable self-heating cycle in main or portable batteries causing dense toxic smoke, high heat, and potential fire blowout.	Isolate battery bus immediately, don oxygen masks at 100% emergency pressure, and execute smoke removal checklist.

Step 3: Avionics, Pitot-Static & Automated Systems

Degradations in automated flight controls and environmental sensors require clear descriptions of reversionary flight control laws and instrument anomalies:

Pitot-Static Tube Blockage: Obstruction of external pitot probes or static ports by ice accumulation or volcanic ash, generating erroneous or conflicting airspeed and altitude indications (unreliable airspeed).
Uncommanded Autopilot Disengagement: Sudden drop-out of automated lateral (LNAV) and vertical (VNAV) flight directors due to sensor disagreement or internal servo trip, requiring immediate manual hand-flying.
Flight Control Law Degradation: Transition of Fly-By-Wire (FBW) flight computers from Normal Law to Alternate or Direct Law, removing automatic flight envelope protections (stall/overspeed protection).
EGPWS (Enhanced Ground Proximity Warning System) Warning: Cockpit alert indicating imminent collision risk with terrain or obstacles ("TERRAIN, PULL UP"), requiring instant maximum thrust escape climb.
TCAS Resolution Advisory (RA): Automated collision avoidance directive commanding immediate climb or descent maneuvers to maintain vertical separation from conflicting traffic.

Standard Radiotelephony: TCAS Resolution Advisory (Doc 4444)

"Frankfurt Radar, Lufthansa 458, TCAS RA."
(Followed by after resolution): "Frankfurt Radar, Lufthansa 458, CLEAR OF CONFLICT, resuming flight level two eight zero."

Step 4: Flight Control Surfaces & Actuator Jamming

Mechanical, aerodynamic, or hydraulic failures impacting primary and secondary control surfaces alter handling characteristics significantly:

Control Abnormality	Mechanical Cause & Effect	Piloting Consideration
Runaway Stabilizer Trim	Uncommanded, continuous motorized rotation of the horizontal stabilizer trim wheel, driving the aircraft nose rapidly up or down.	Immediately disengage autopilot, grasp trim wheel manually, and actuate electric stab trim cutout switches.
Flap / Slat Asymmetry	Mechanical jam causing high-lift surfaces on one wing to stop while the opposite side continues traveling, inducing heavy uncommanded roll.	Leave flaps in current position; fly flapless/partial-flap landing speed profile with extended runway length.
Aileron / Rudder Jam	Physical binding of cables or actuators preventing deflection of primary roll or yaw control surfaces.	Use alternate control methods: differential engine thrust for directional yaw and rudder/spoilers for roll authority.
Spoiler / Speedbrake Float	Inability of hydraulic actuators to hold spoiler panels flush against the upper wing surface during high-speed cruise.	Causes parasite drag rise, airframe buffeting, and slight aerodynamic lift dump.

Step 5: Landing Gear, Braking & Ground Deceleration Failures

Touchdown and rollout safety depends on mechanical downlocks, anti-skid transducers, and carbon brake assemblies:

Problem / Malfunction	Operational Nature	Aerodrome & Tactical Consequence
Gravity / Alternate Gear Extension	Free-fall deployment of the landing gear using mechanical uplock releases and aerodynamic gravity fall when main hydraulic extension fails.	Landing gear cannot be retracted once extended; causes elevated drag and fuel consumption.
Anti-Skid System Inoperative	Failure of wheel speed sensors or modulator valves that prevent wheel lockup during aggressive braking on wet or contaminated runways.	Increases required landing roll distance significantly; risks multiple blown tires upon maximum manual brake application.
Hot Brakes / Fuse Plug Release	Excessive thermal accumulation in brake disks after rejected takeoff (RTO), melting thermal fuse plugs to deflate tires safely and prevent wheel explosion.	Aircraft must hold on taxiway or remote stand with brake fans running; airport fire services must inspect wheels.
Nose-Wheel Steering (NWS) Failure	Loss of hydraulic steering actuator control on the nose gear assembly, eliminating flight deck tiller steering capability.	Aircraft cannot vacate the runway under its own power; requires a tow truck and tug assistance after stopping on the runway.

Step 6: Practical Oral Application & Model Exam Drills

Study these model spoken responses to observe how technical aviation terms are structured under exam conditions:

Drill 1: Explaining a Hydraulic & Flight Control Problem (Part 3 Role-Play)

"Vienna Radar, Austrian 224, we have a dual hydraulic failure affecting our yellow and green circuits. As a result, our flight control system has degraded to Alternate Law and we are unable to extend our trailing edge flaps. We request twenty track miles of straight-in final approach for runway two-niner and emergency ground services standing by on rollout."

Drill 2: Describing Landing Gear Fault from a Photograph (Part 2 Picture)

"In the photograph, we see ground engineers examining the main gear bogie of an airliner. The thermal fuse plugs have released due to severe brake overheating following an aborted high-speed takeoff. As a consequence, both main tires are completely deflated, and the maintenance crew is using infrared thermography sensors to verify brake temperature dissipation before towing."

Drill 3: Fly-By-Wire vs. Conventional Cable Control Discussion (Part 4 Discussion)

"While modern Fly-By-Wire architectures reduce airframe structural weight and integrate flight envelope protection against stalls and overstressing, they introduce potential failure modes related to computer bus disagreements and flight control law degradation. Pilots must remain proficient in manual handling techniques when flight computers drop to Direct Law."