✈️ The Hidden Danger in Aerobatics: Understanding the Push–Pull Effect

A Human Factors explainer for beginners, aviation fans, and experts

⭐ Introduction

Combat aircrafts like the Tejas are required to perform dynamic maneuvers during combat missions. One of the maneuvers is:

🔄 A smooth roll

🔽 A sustained negative-G segment

🔼 Followed by a rapid positive-G pull-up

This article uses this moment to explain one of aviation physiology’s most important hazards:

the push–pull effect.

The result of sustained negative G maneuver reduces the positive G tolerance significantly. This phenomenon has been documented for decades in research from USAF, NATO, Canadian Forces, RAF, and the Indian Air Force.

Understanding it helps everyone — from lay readers to aviators — appreciate the limits of the human body.

🚀 What Is the Push–Pull Effect?

🤚 Step 1 — PUSH (Negative-G / −Gz)

Blood is forced upward toward the head:

Brain blood vessels dilate (widen) Neck veins engorge The body tries to “reduce pressure” by relaxing vessels

📌 Citation:

“Tolerance for +Gz decreases markedly when +Gz is preceded by mild −Gz.”

(USAF Balldin)

✋ Step 2 — PULL (Positive-G / +Gz)

When the aircraft suddenly pulls up:

G-forces pull blood downward BUT the brain’s vessels are still wide open from the −G Blood drains rapidly, like water through a wide pipe Resulting in: 👁️ Grey-out 🌑 Blackout 😵 ALOC (Almost Loss of Consciousness) 🧨 G-LOC (Loss of Consciousness)

📌 Citation:

“+2.25G preceded by −2G produces significantly reduced blood pressure in +G.”

(NATO STO HFM-309)

🧠 Expert Breakdown of the Physiology

🔍 During −Gz

Cerebral arteries dilate Baroreceptors (pressure sensors) turn down sympathetic tone Vessel walls relax The system becomes under-pressurised for the next stage

🔍 During the transition

Reflex systems take 1–3 seconds to respond This delay is called baroreflex lag

🔍 During +Gz

The body needs tight vessels to hold blood up But vessels are still dilated Brain perfusion collapses Leading to rapid visual loss and possible G-LOC

📌 Citation:

IAF centrifuge research: “ALOC and G-LOC involve ~10–12 seconds of incapacitation.”

(IAF IAM)

🌍 What the World’s Research Shows

🇨🇦 Canadian Forces

A review of 284 military jet accidents found:

5 accidents + 2 incidents likely linked to push–pull physiology Pilots were 23–30 years old

🇺🇸 USAF

USAF aeromedical studies confirm:

Push–pull sharply reduces +G tolerance Contributed to several fatal accidents

🇬🇧 RAF / AAIB

Findings in Hawk and fast-jet accidents:

Unloading or mild −G before a pull-up can trigger unexpected G-LOC Display flying rules were tightened as a result

🌐 NATO

Controlled experiments show:

Even mild −G → +G sequences reduce brain blood pressure Longer −G exposure worsens the danger

🇮🇳 Indian Air Force

IAF IAM analysis of 42 centrifuge G-LOC/ALOC episodes found:

Mean pilot age ~26 years Incapacitation lasted 10–12 seconds

🔍 Myth-Busting: “Younger Pilots Tolerate G Better”

Not necessarily.

The numbers say otherwise:

Canadian push–pull pilots: 23–30 years IAF G-LOC subjects: average 26 years

Age within the fighter pilot range (20s–40s) is NOT a major factor.

Hydration, fatigue, heat stress, and −G duration matter more.

🛡️ Human Factors View: Why This Isn’t “Pilot Error”

Many push–pull accidents look like pilot mistakes from the outside.

But Human Factors tells a different story:

✔ It happens faster than conscious control

✔ It defeats even elite pilots

✔ It stems from biology, not skill

✔ It’s a predictable human limitation

This is why Safety Matters Foundation consistently argues for non-punitive accident investigation to determine the root causes:

“Accident learning requires a just culture framework.”

💡 Key Takeaways

For general readers

The push–pull effect is a real, well-documented risk. It involves the body being unable to adjust quickly from −G to +G.

For aviation fans

Even ace pilots are vulnerable — biology sets the limits.

For pilots & HF professionals

Baroreflex delay is central. ALOC = as operationally dangerous as G-LOC. Expect 10–12 seconds of incapacitation.

For safety leaders

Blame is counter-productive. Systemic solutions save lives. Education about physiology is essential.

📚 Citations

Canadian Forces Accident Review (Push–Pull)

USAF Balldin, Acceleration Effects on Fighter Pilots

IAF IAM ALOC–G-LOC Centrifuge Study

NATO STO HFM-309 Push–Pull Experiments

Safety Matters Foundation – Just Culture Advocacy