Red Arrows pilot’s view through a Hawk canopy over RAF Scampton

Canopy Detonating Cord: Why Some Jets Shatter the Canopy to Eject

by Max Grünwald | Sep 28, 2026 | Aviación militar | 0 comments

Look closely at the canopy of a Red Arrows Hawk, a Harrier or a T-6 Texan II and you will see thin, wavy lines running across the transparency like a child's drawing of lightning. They are not cracks, and they are not heating wires. They are explosives.

That wiggly line is miniature detonating cord, MDC for short. In an ejection it fires a fraction of a second before the seat, shattering the canopy so the pilot can go straight up through it instead of waiting for the canopy to be thrown clear. It is one of the cleverest and least-known parts of a modern escape system.

Datos rápidos

Qué es: Miniature detonating cord (MDC), or a flexible linear shaped charge, embedded in or fixed to the canopy
What it does: Shatters the canopy a few milliseconds before the ejection seat fires
Por qué: Waiting for a canopy to be jettisoned is too slow at low level, in a hover or at low speed
Origen: Developed for the Harrier family, which might need to eject from a hover
Aircraft using it: Including the BAE Hawk, Harrier family and T-6 Texan II, according to published descriptions
Alternative: Canopy jettison with thrusters or rockets, or seat-top breakers that punch through the canopy

The Problem With Throwing the Canopy Away

In most fighters, ejection starts by getting rid of the canopy. Explosive or propellant devices unlatch it, then thrusters or small rockets throw it back and away. Only once the canopy has moved clear does the seat fire, because a seat and a canopy colliding is a disaster.

That takes time, and the time is not fixed. A NASA Langley study of canopy fracturing pointed out that how quickly a canopy clears depends on the aircraft's attitude and forward speed. With the nose pitched down or at low speed, there is little airflow to help pull the canopy away.

“Through-canopy crew egress, such as in the Harrier (AV-8B) aircraft, expands escape envelopes by reducing seat ejection delays in waiting for canopy jettison.”

Laurence J. Bement, NASA Langley Research Center — “Explosive Fracturing of an F-16 Canopy for Through-Canopy Crew Egress,” SAFE Symposium, 2000

Marines handling the canopy of an AV-8B Harrier — Flight safety equipment mechanics of Marine Attack Squadron 211 work on an AV-8B Harrier canopy at Eielson Air Force Base, Alaska, in April 2010. Photo: Lance Cpl. Sean Dennison, USMC, public domain

Born in the Hover

The Harrier made the problem impossible to ignore. A jet that can hover might need its pilot to eject with no forward speed at all, and a jettisoned canopy could hang in the air right where the seat was about to go. The answer, developed for the Harrier family, was to destroy the canopy in place instead.

The explosive cord is laid in a pattern across the acrylic. When the pilot pulls the ejection handle, the cord detonates and shatters the canopy over the seat a few milliseconds before the seat is launched. On the Martin-Baker Mk.10 seat, for example, operating the firing handle initiates the canopy MDC first, then fires the seat's main gun.

Where You Will Find It

Canopy destruct systems are used on the BAE Hawk and the Harrier line, and on the Beechcraft T-6 Texan II, which Wikipedia notes is fitted with Martin-Baker Mk.16 seats and a canopy-fracturing system. The pattern of the cord is designed so that the canopy breaks where the seat needs a path, while large pieces are kept out of the cockpit.

Some aircraft combine approaches. The T-6 also carries breakers on the seat in case the MDC fails to fire, and the A-10 has canopy breakers on either side of its headrest in case its canopy fails to jettison. Other types, the NASA paper notes, such as the F-15, use frangible acrylic canopies and seats designed to punch through as a backup.

AV-8B Harrier IIs at sunrise on USS Tarawa — The sun rises behind AV-8B Harrier IIs on the flight deck of USS Tarawa in December 2007. The Harrier family pioneered canopy-shattering escape. Photo: U.S. Navy, public domain

The Polycarbonate Problem

MDC works well on acrylic, which shatters. Modern bird-strike-resistant canopies are made of tough polycarbonate, which does not. The NASA Langley study found that heavy, high-strength polycarbonate canopies had not only increased jettison times but had made seat penetration impossible, and it set out to show that even an F-16 canopy could be explosively fractured for through-canopy ejection.

The study reported that all of its goals were met in a full-scale test, including operating in under 10 milliseconds and keeping major pieces from falling into the cockpit. For most pilots, the lines on the canopy are just part of the view. For the few who ever need them, they are the first thing that happens after the handle is pulled.

“In addition to expanding crew escape envelopes, this canopy fracture approach offers the potential for reducing system complexity, weight and cost, while increasing overall reliability, compared to current canopy jettison approaches.”

Laurence J. Bement, NASA Langley Research Center — SAFE Symposium paper, 2000

Sources: L.J. Bement, NASA Langley Research Center, “Explosive Fracturing of an F-16 Canopy for Through-Canopy Crew Egress” (SAFE Symposium, 2000); Wikipedia (Ejection seat; Martin-Baker Mk.10; Beechcraft T-6 Texan II); U.S. Navy, USMC and UK MOD image records.

Preguntas frecuentes

What are the wavy lines on a fighter jet canopy?

On aircraft such as the BAE Hawk, Harrier and T-6 Texan II, the wavy lines on the canopy are miniature detonating cord (MDC). In an ejection the cord detonates and shatters the canopy a few milliseconds before the seat fires, so the pilot can eject straight through it.

What is miniature detonating cord (MDC)?

Miniature detonating cord is a thin explosive cord laid in a pattern across an aircraft canopy. When the ejection handle is pulled, it fires first and fractures the canopy over the seat, removing the delay of waiting for the canopy to be jettisoned.

Why do some jets shatter the canopy instead of jettisoning it?

Jettisoning a canopy takes time and depends on aircraft attitude and airspeed. At low speed, in a hover or in a nose-down attitude, the canopy may clear slowly. Shattering it in place lets the seat fire almost immediately, expanding the conditions in which ejection is survivable.

Which aircraft use canopy-shattering ejection systems?

Canopy destruct systems were developed for the Harrier family and are used on the BAE Hawk and the Beechcraft T-6 Texan II, among others, according to published descriptions. Many other fighters jettison their canopy instead, sometimes with seat-top breakers as a backup.

Can a polycarbonate canopy be shattered for ejection?

Tough polycarbonate canopies are much harder to break than acrylic ones. A NASA Langley study presented in 2000 demonstrated a method of explosively fracturing an F-16 polycarbonate canopy in under 10 milliseconds to allow through-canopy ejection in a full-scale test.